Propagation path response estimation and interference canceling using spread-spectrum pilot signal in multi-feeder link of HAPS

ABSTRACT

A downlink interference is dynamically suppressed in a multi-feeder link of a same frequency between an aerial-floating type communication relay apparatus and plural gateway (GW) stations with a simple configuration. A plurality of pilot signals, which are spectrally spread using a plurality of spread codes orthogonal to each other, are transmitted and received between the relay communication station of the aerial-staying type communication relay apparatus and plural GW stations, a propagation path response between plural GW stations and an antenna for feeder link of the communication relay apparatus in a transmission signal band of the feeder link is estimated based on reception results in which the plural pilot signals are spectrally inverse-spread, plural weights respectively corresponding to the plural of GW stations are calculated based on the plural propagation path responses, and with respect to each of the plural GW stations, a signal to be transmitted and received via a directional beam corresponding to another GW station is multiplied by the weight corresponding to the other GW station and subtracted from a signal to be transmitted and received via the directional beam corresponding to the GW station.

TECHNICAL FIELD

The present invention relates to a propagation-path response measurement and an interference canceling in a multi-feeder link of an aerial-floating type radio relay apparatus such as a HAPS suitable for constructing a three-dimensional network.

BACKGROUND ART

There is conventionally known a communication relay apparatus such as a high altitude platform station (HAPS) (also referred to as “high altitude pseudo satellite”) that can float and stay in an airspace (for example, see Patent Literature 1). A communication line in this aerial-floating type communication relay apparatus is configured with a feeder link between the communication relay apparatus and a gateway (GW) station on a mobile communication network side, and a service link between the communication relay apparatus and a terminal apparatus.

CITATION LIST Patent Literature

-   Patent Literature 1: U.S. Patent Application Publication No.     2016/0046387.

SUMMARY OF INVENTION Technical Problem

Since a communication capacity of the service link of the aerial-floating type communication relay apparatus (hereinafter referred to as “upper-air relay apparatus”) depends on a communication capacity of a feeder link of a relay frequency, an effective use of the frequency of feeder link is essential. Therefore, it is considered of a method in which plural GW stations on the ground are disposed at locations separated from each other to form a multi-feeder link that transmits and receives different feeder link signals on the same frequency from each GW station. However, unlike the fixed station, the upper-air relay apparatus flies around in a predetermined airspace, so that a dynamic interference may occur in the multi-feeder link of the same frequency between the upper-air relay apparatus and the plural GW stations, and there is a problem that it is desired to realize a suppression of dynamic interference in the multi-feeder link with a simple configuration.

Solution to Problem

A system according to an aspect of the present invention is a system comprising an aerial-staying type communication relay apparatus including a relay communication station that relays a radio communication of a terminal apparatus. The system comprises plural gateway stations that are time-synchronized with each other and transmit and receive relay signals different from each other on a same frequency in a feeder link to and from the relay communication station of the aerial-staying type communication relay apparatus, means for transmitting and receiving a plurality of pilot signals spread spectrally using a plurality of spreading codes orthogonal to each other, between the relay communication station and the plural gateway stations, means for estimating a propagation path response between the plural gateway stations and an antenna for feeder link of the communication relay apparatus in a transmission signal band of the feeder link, based on reception results of spectral inverse-spreading of the plural pilot signals, means for calculating plural weights respectively corresponding to the plural gateway stations based on the plural propagation path responses, and means for subtracting, from a signal to be transmitted and received via a directional beam corresponding to the gateway station, a signal to be transmitted and received via the directional beam corresponding to the other gateway station that is multiplied by the weight corresponding to the other gateway station, with respect to each of the plural gateway stations.

In the foregoing system, the relay communication station may comprise a feeder-link communication section that transmits and receives relay signals different from each other on a same frequency in the feeder link to and from the plural gateway stations, and an interference suppression section that suppresses an interference between plural feeder links formed with the plural gateway stations, the plural gateway stations may transmit a plurality of spread pilot signals that are spectrally spread with a plurality of transmission-side spreading codes orthogonal to each other, to the relay communication station, the feeder-link communication section of the relay communication station may receive the plurality of spread pilot signals from the plural gateway stations and may spectrally inverse-spread reception signals of the plural spread pilot signals with a reception-side spreading code corresponding to the transmission-side spreading code, and the interference suppression section of the relay communication station may estimate a propagation path response between the plural gateway stations and the antenna for feeder link of the communication relay apparatus in the transmission signal band of the feeder link, based on reception results of plurality of inverse-spread pilot signals that are spectrally inverse-spread, calculate plural weights respectively corresponding to the plural gateway stations based on the plural propagation path responses, and subtract, from a reception signal received by the directional beam corresponding to the gateway station, a reception signal received by the directional beam corresponding to the other gateway station that is multiplied by the weight corresponding to the other gateway station, with respect to each of the plural gateway stations.

In the foregoing system, the relay communication station may comprise a feeder-link communication section that transmits and receives relay signals different from each other on the same frequency in the feeder link to and from the plural gateway stations, and an interference suppression section that suppresses an interference between plural feeder links formed with the plural gateway stations, the feeder-link communication section of the relay communication station may transmit a plurality of spread pilot signals that are spectrally spread with a plurality of transmission-side spreading codes orthogonal to each other, the plural gateway stations may receive the plurality of spread pilot signals from the relay communication station, and spectrally inverse-spread reception signals of the plurality of spread pilot signals with a reception-side spreading code corresponding to the transmission-side spreading code, any one of the gateway stations of the plural gateway stations or a common apparatus common to each gateway station may estimate plural propagation path responses between the gateway station and an antenna for feeder link of the communication relay apparatus in a transmission signal band of the feeder link, based on reception results of the plurality of inverse-spread pilot signals that are spectrally inverse-spread, and transmit estimation results of the propagation path responses to the relay communication station, the feeder-link communication section of the relay communication station may receive the plural propagation path responses transmitted from the any one of the gateway stations or the common apparatus, and the interference suppression section of the relay communication station may calculate a weight for suppressing an interference signal that causes an interference by a transmission signal transmitted from the relay communication station to the gateway station and received by another gateway station, based on the plural propagation path responses, with respect to each of the plural gateway stations, and add or subtract, for the transmission signal to be transmitted to the gateway station, a transmission signal to be transmitted to the other gateway station that is multiplied by the weight corresponding to the other gateway station, with respect to each of the plural gateway stations.

In the foregoing system, the relay communication station may comprise a feeder-link communication section that transmits and receives relay signals different from each other on the same frequency in the feeder link to and from the plural gateway stations, and an interference suppression section that suppresses an interference between plural feeder links formed with the plural gateway stations, the feeder-link communication section of the relay communication station may transmit a plurality of spread pilot signals that are spectrally spread with a plurality of transmission-side spreading codes orthogonal to each other, the plural gateway stations may receive the plurality of spread pilot signals from the relay communication station, spectrally inverse-spread reception signals of the plurality of spread pilot signals with a reception-side spreading code corresponding to the transmission-side spreading code, and transmit reception results of the plurality of inverse-spread pilot signals that are spectrally inverse-spread, to the relay communication station, the feeder-link communication section of the relay communication station may receive the reception results of the plurality of inverse-spread pilot signals transmitted from each of the plural gateway stations, and the interference suppression section of the relay communication station may estimate plural propagation path responses between the gateway station and an antenna for feeder link of the communication relay apparatus in a transmission signal band of the feeder link, based on the reception results of the plural pilot signals received from each of the plural gateway stations, calculate a weight for suppressing an interference signal that causes an interference by a transmission signal transmitted from the relay communication station to the gateway station and received by another gateway station, based on estimation results of the plural propagation path responses, with respect to each of the plural gateway stations, and add or subtract, for the transmission signal to be transmitted to the gateway station, a transmission signal to be transmitted to the other gateway station that is multiplied by the weight corresponding to the other gateway station, with respect to each of the plural gateway stations.

In the foregoing system, the relay communication station may comprise a feeder-link communication section that transmits and receives relay signals different from each other on the same frequency in the feeder link to and from the plural gateway stations, and an interference suppression section that suppresses an interference between plural feeder links formed with the plural gateway stations, the feeder-link communication section of the relay communication station may transmit a plurality of spread pilot signals that are spectrally spread with a plurality of transmission-side spreading codes orthogonal to each other, the plural gateway stations may receive the plurality of spread pilot signals from the relay communication station, and spectrally inverse-spread reception signals of the plurality of spread pilot signals with a reception-side spreading code corresponding to the transmission-side spreading code, any one of the gateway stations of the plural gateway stations or a common apparatus common to each gateway station may estimate plural propagation path responses between the gateway station and an antenna for feeder link of the communication relay apparatus in a transmission signal band of the feeder link, based on reception results of the plurality of inverse-spread pilot signals that are spectrally inverse-spread, calculate a weight for suppressing an interference signal that causes an interference by a transmission signal transmitted from the relay communication station to the gateway station and received by another gateway station, based on estimation results of the plural propagation path responses, with respect to each of the plural gateway stations, and transmit a calculation result of the weight to the relay communication station, the feeder-link communication section of the relay communication station may receive calculation results of the plural weights transmitted from the any one of the gateway stations or the common apparatus, and the interference suppression section of the relay communication station may add or subtract, for the transmission signal to be transmitted to the gateway station, a transmission signal to be transmitted to the other gateway station that is multiplied by the weight corresponding to the other gateway station, with respect to each of the plural gateway stations.

In the foregoing system, the relay communication station may comprise a feeder-link communication section that transmits and receives relay signals different from each other on the same frequency in the feeder link to and from the plural gateway stations, and an interference suppression section that suppresses an interference between plural feeder links formed with the plural gateway stations,

the plural gateway stations may transmit a plurality of spread pilot signals that are spectrally spread with a plurality of transmission-side spreading codes orthogonal to each other, to the relay communication station, the feeder-link communication section of the relay communication station may receive the plurality of spread pilot signals from the plural gateway stations, and spectrally inverse-spread reception signals of the plurality of spread pilot signals with a reception-side spreading code corresponding to the transmission-side spreading code, and the interference suppression section of the relay communication station may estimate plural propagation path responses between the plural gateway stations and an antenna for feeder link of the communication relay apparatus in a transmission signal band of the feeder link, based on reception results of the plurality of inverse-spread pilot signals that are spectrally inverse-spread, calculate a weight for suppressing an interference signal that causes an interference by a transmission signal transmitted from the relay communication station to the gateway station and received by another gateway station, based on the plural propagation path responses, with respect to each of the plural gateway stations, and add or subtract, for the transmission signal to be transmitted to the gateway station, a transmission signal to be transmitted to the other gateway station that is multiplied by the weight corresponding to the other gateway station, with respect to each of the plural gateway stations.

In the foregoing system, the relay communication station may transmit a plurality of spread pilot signals that are spectrally spread with a plurality of transmission-side spreading codes orthogonal to each other, the plural gateway stations may receive the plurality of spread pilot signals from the relay communication station, spectrally inverse-spread with a reception-side spreading code corresponding to the transmission-side spreading code, estimate plural propagation path responses between the gateway stations and an antenna for feeder link of the communication relay apparatus in a transmission signal band of the feeder link, based on reception results of the plurality of inverse-spread pilot signals that are spectrally inverse-spread, calculate a weight for suppressing an interference signal that causes an interference by a transmission signal transmitted from the relay communication station to the gateway station and received by another gateway station, based on the plural propagation path responses, and add or subtract, for the reception signal received by the gateway station, a reception signal received by the other gateway station that is multiplied by the weight corresponding to the other gateway station.

A relay communication station according to another aspect of the present invention is a relay communication station that is incorporated in an aerial-staying type communication relay apparatus and relays radio communication of a terminal apparatus. The relay communication station comprises a feeder-link communication section that transmits and receives relay signals different from each other on a same frequency in a feeder link to and from plural gateway stations that are time-synchronized with each other, and an interference suppression section that suppresses an interference between plural feeder links formed with the plural gateway stations. The feeder-link communication section receives a plurality of spread pilot signals that are spectrally spread with a plurality of transmission-side spreading codes orthogonal to each other, from the plural gateway stations, and inverse-spreads reception signals of the plurality of spread pilot signals with a reception-side spreading code corresponding to the transmission-side spreading code, and the interference suppression section estimates propagation path responses between the plural gateway stations and an antenna for feeder link of the communication relay apparatus in a transmission signal band of the feeder link, based on reception results of the plurality of inverse-spread pilot signals that are spectrally inverse-spread, calculates plural weights respectively corresponding to the plural gateway stations based on the plural propagation path responses, and subtracts, from a reception signal received by the directional beam corresponding to the gateway station, a reception signal received by the directional beam corresponding to the other gateway station that is multiplied by the weight corresponding to the other gateway station, with respect to each of the plural gateway stations.

A relay communication station according to yet another aspect of the present invention is a relay communication station that is incorporated in an aerial-staying type communication relay apparatus and relays radio communication of a terminal apparatus. The relay communication station comprises a feeder-link communication section that transmits and receives relay signals different from each other on a same frequency in a feeder link to and from plural gateway stations that are time-synchronized with each other, and an interference suppression section that suppresses an interference between plural feeder links formed with the plural gateway stations. The feeder-link communication section transmits a plurality of spread pilot signals that are spectrally spread with a plurality of transmission-side spreading codes orthogonal to each other, to the plural gateway stations, and receives estimation results of plural propagation path responses between the gateway stations and an antenna for feeder link of the communication relay apparatus in a transmission signal band of the feeder link, wherein the estimation results are estimated based on the reception signals of the plural inverse-spread pilot signals that are spectrally inverse-spread with a reception-side spreading code corresponding to the transmission-side spreading code by any one of the plural gateway stations or a common apparatus common to each gateway station, and the interference suppression section calculates a weight for suppressing an interference signal that causes an interference by a transmission signal transmitted from the relay communication station to the gateway station and received by another gateway station, based on the plural propagation path responses received from the any one of the gateway stations or the common apparatus, with respect to each of the plural gateway stations, and adds or subtracts, for a transmission signal to be transmitted to the gateway station, a transmission signal to be transmitted to the other gateway station that is multiplied by the weight corresponding to the other gateway station, with respect to each of the plural gateway stations.

A relay communication station according to yet another aspect of the present invention is a relay communication station that is incorporated in an aerial-staying type communication relay apparatus and relays radio communication of a terminal apparatus. The relay communication station comprises a feeder-link communication section that transmits and receives relay signals different from each other on a same frequency in a feeder link to and from plural gateway stations that are time-synchronized with each other, and an interference suppression section that suppresses an interference between plural feeder links formed with the plural gateway stations. The feeder-link communication section transmits a plurality of spread pilot signals that are spectrally spread with a plurality of transmission-side spreading codes orthogonal to each other, to the plural gateway stations, and receives reception results of the plurality of inverse-spread pilot signals, wherein the plural gateway stations spectrally inverse-spread the reception signal of the spread pilot signal with a reception-side spreading code corresponding to the transmission-side spreading code. The interference suppression section estimates plural propagation path responses between the gateway stations and an antenna for feeder link of the communication relay apparatus in a transmission signal band of the feeder link, based on reception results of the plurality of inverse-spread pilot signals, calculates a weight for suppressing an interference signal that causes an interference by a transmission signal transmitted from the relay communication station to the gateway station and received by another gateway station, based on estimation results of the plural propagation path responses, with respect to each of the plural gateway stations, and adds or subtracts for the transmission signal to be transmitted to the gateway station, a transmission signal to be transmitted to the other gateway station that is multiplied by the weight corresponding to the other gateway station, with respect to each of the plural gateway stations.

A relay communication station according to yet another aspect of the present invention is a relay communication station that is incorporated in an aerial-staying type communication relay apparatus and relays radio communication of a terminal apparatus. The relay communication station comprises a feeder-link communication section that transmits and receives relay signals different from each other on a same frequency in a feeder link to and from plural gateway stations that are time-synchronized with each other, and an interference suppression section that suppresses an interference between plural feeder links formed with the plural gateway stations. The feeder-link communication section transmits a plurality of spread pilot signals that are spectrally spread with a plurality of transmission-side spreading codes orthogonal to each other, to the plural gateway stations, and receives a calculation result of a weight for suppressing an interference signal that causes an interference by a transmission signal transmitted from the relay communication station to the gateway station and received by another gateway station, wherein the weight is calculated based on the reception signals of the plurality of inverse-spread pilot signals that are spectrally inverse-spread with a reception-side spreading code corresponding to the transmission-side spreading code by any one of the plural gateway stations or a common apparatus common to each gateway station, with respect to each of the plural gateway stations. The interference suppression section adds or subtracts, for the transmission signal to be transmitted to the gateway station, a transmission signal to be transmitted to another gateway station that is multiplied by the weight corresponding to the other gateway station, with respect to each of the plural gateway stations.

A relay communication station according to yet another aspect of the present invention a relay communication station that is incorporated in an aerial-staying type communication relay apparatus and relays radio communication of a terminal apparatus. The relay communication station comprises a feeder-link communication section that transmits and receives relay signals different from each other on a same frequency in a feeder link to and from plural gateway stations that are time-synchronized with each other, and an interference suppression section that suppresses an interference between plural feeder links formed with the plural gateway stations. The feeder-link communication section receives spread pilot signals that are spectrally spread with a plurality of transmission-side spreading codes orthogonal to each other, from the plural gateway stations, and spectrally inverse-spreads reception signals of the plurality of spread pilot signals with a reception-side spreading code corresponding to the transmission-side spreading code. The interference suppression section estimates plural propagation path responses between the plural gateway stations and an antenna for feeder link of the communication relay apparatus in a transmission signal band of the feeder link, based on reception results of the plural inverse-spread pilot signals that are spectrally inverse-spread, calculates a weight for suppressing an interference signal that causes an interference by a transmission signal transmitted from the relay communication station to the gateway station and received by another gateway station, based on the plural propagation path responses, with respect to each of the plural gateway stations, and adds or subtracts for the transmission signal to be transmitted to the gateway station, a transmission signal to be transmitted to the other gateway station that is multiplied by the weight corresponding to the other gateway station, with respect to each of the plural gateway stations.

An aerial-staying type communication relay apparatus according to yet another aspect of the present invention includes any one of the above-mentioned relay communication stations.

A gateway station according to yet another aspect of the present invention is a gateway station that is incorporated in an aerial-staying type communication relay apparatus and transmits and receives relay signals different from each other on a same frequency in a feeder link to and from a relay communication station that relays radio communication of a terminal apparatus. The gateway station is time-synchronized with another gateway station that transmits and receives relay signals on the same frequency in the feeder link to and from the relay communication station. The gateway station receives a plurality of spread pilot signals that are spectrally spread with a plurality of transmission-side spreading codes orthogonal to each other, from the relay communication station, spectrally inverse-spreads reception signals of the spread pilot signals with a reception-side spreading code corresponding to the transmission-side spreading code, receives reception results of a plurality of inverse-spread pilot signals from the other gateway station, wherein the other gateway station receives the plural spread pilot signals and spectrally inverse-spreads the plural spread pilot signals with a reception-side spreading code corresponding to the transmission-side spreading code, estimates plural propagation path responses between own gateway station and the other gateway station and an antenna for feeder link of the communication relay apparatus in a transmission signal band of the feeder link, based on the reception results of the plurality of inverse-spread pilot signals of own gateway station and the other gateway station, and transmits estimation results of the propagation path responses to the relay communication station.

A gateway station according to yet another aspect of the present invention is a gateway station that is incorporated in an aerial-staying type communication relay apparatus and transmits and receives relay signals different from each other on a same frequency in a feeder link to and from a relay communication station that relays radio communication of a terminal apparatus. The gateway station is time-synchronized with another gateway station that transmits and receives relay signals on the same frequency in the feeder link to and from the relay communication station. The gateway station receives a plurality of spread pilot signals that are spectrally spread with a plurality of transmission-side spreading codes orthogonal to each other, from the relay communication station, spectrally inverse-spreads the reception signal of the spread pilot signal with a reception-side spreading code corresponding to the transmission-side spreading, receives reception results of the plural inverse-spread pilot signals from the other gateway station, wherein the other gateway station receives the plural spread pilot signals and spectrally inverse-spreads the plural spread pilot signals with a reception-side spreading code corresponding to the transmission-side spreading code, estimates plural propagation path responses between own gateway station and the other gateway station and an antenna for feeder link of the communication relay apparatus in a transmission signal band of the feeder link, based on the reception results of the plural inverse-spread pilot signals of the own gateway station and the other gateway station, and calculates a weight for suppressing an interference signal that causes an interference by a transmission signal transmitted from the relay communication station to the gateway station and received by another gateway station, based on the estimation results of the plural propagation path responses, with respect to each of the plural gateway stations.

A gateway station according to yet another aspect of the present invention is a gateway station that is incorporated in an aerial-staying type communication relay apparatus and transmits and receives relay signals different from each other on a same frequency in a feeder link to and from a relay communication station that relays radio communication of a terminal apparatus. The gateway station is time-synchronized with another gateway station that transmits and receives relay signals on the same frequency in the feeder link to and from the relay communication station. The gateway station receives a plurality of spread pilot signals that are spectrally spread with a plurality of transmission-side spreading codes orthogonal to each other, from the relay communication station, spectrally inverse-spreads the reception signal of the spread pilot signal with a reception-side spreading code corresponding to the transmission-side spreading code, receives reception results of a plurality of inverse-spread pilot signals from the other gateway station, wherein the other gateway station receives the plurality of spread pilot signals and spectrally inverse-spreads the plural spread pilot signals with a reception-side spreading code corresponding to the transmission-side spreading code, estimates plural propagation path responses between own station and the other gateway station and an antenna for feeder link of the communication relay apparatus in a transmission signal band of the feeder link, based on the reception results of the plurality of inverse-spread pilot signals of the own gateway station and the other gateway station, calculates a weight for suppressing an interference signal that causes an interference by a transmission signal transmitted from the relay communication station to the own gateway station and received by another gateway station, based on the estimation results of the plural propagation path responses, and adds or subtracts, for a reception signal received by the own gateway station, a reception signal received by the other gateway station that is multiplied by the weight corresponding to the other gateway station.

An interference suppression method according to yet another aspect of the present invention is an interference suppression method in a feeder link between a relay communication station and plural gateway stations, wherein the relay communication station is incorporated in an aerial-staying type communication relay apparatus and relays radio communication of a terminal apparatus, and the plural gateway stations are time-synchronized with each other to transmit and receive relay signals different from each other on a same frequency. The interference suppression method comprises transmitting and receiving a plurality of pilot signals that are spectrally spread using a plurality of spreading codes orthogonal to each other between the relay communication station and the plural gateway stations, estimating a propagation path response between the plural gateway stations and an antenna for feeder link of the communication relay apparatus in a transmission signal band of the feeder link, based on reception results of spectral inverse-spreading the plurality of pilot signals, calculating plural weights respectively corresponding to the plural gateway stations based on the plural propagation path responses, and subtracting, from a signal to be transmitted and received via a directional beam corresponding to the gateway station, a signal to be transmitted and received via the directional beam corresponding to the other gateway station that is multiplied by the weight corresponding to the other gateway station, with respect to each of the plural gateway stations.

A program according to yet another aspect of the present invention is a program executed by a computer or a processor installed in a relay communication station that is incorporated in an aerial-staying type communication relay apparatus and relays radio communication of a terminal apparatus. The program includes a program code for receiving a plurality of spread pilot signals that are spectrally spread with a plurality of transmission-side spreading codes orthogonal to each other, from plural gateway stations that are time-synchronized with each other, a program code for inverse-spreading by spectrally inverse-spreading reception signals of the plurality of spread pilot signals with a reception-side spreading code corresponding to the transmission-side spreading code, a program code for estimating propagation path responses between the plural gateway stations and an antenna for feeder link of the communication relay apparatus in a transmission signal band of a feeder link, based on the reception results of the plurality of inverse-spread pilot signals that are spectrally inverse-spread, a program code for calculating plural weights respectively corresponding to the plural gateway stations based on the plural propagation path responses, and a program code for subtracting, from a reception signal received by the directional beam corresponding to the gateway station, a reception signal received by the directional beam corresponding to the other gateway station that is multiplied by the weight corresponding to the other gateway station, with respect to each of the plural gateway stations.

A program according to yet another aspect of the present invention is a program executed by a computer or a processor installed in a relay communication station that is incorporated in an aerial-staying type communication relay apparatus and relays radio communication of a terminal apparatus. The program comprises a program code for transmitting a plurality of spread pilot signals that are spectrally spread with a plurality of transmission-side spreading codes orthogonal to each other, to plural gateway stations that are time-synchronized with each other, a program code for receiving estimation results of plural propagation path responses between the gateway stations and an antenna for feeder link of the communication relay apparatus in a transmission signal band of a feeder link, wherein the estimation results are estimated by any one of the plural gateway stations or a common apparatus common to each gateway station based on reception results of the plurality of inverse-spread pilot signals that are spectrally inverse-spread with a reception-side spreading code corresponding to the transmission-side spreading code, a program code for calculating a weight for suppressing an interference signal that causes an interference by a transmission signal transmitted from the relay communication station to the gateway station and received by another gateway station, based on the plural propagation path responses received from any one of the gateway stations or the common apparatus, with respect to each of the plural gateway stations, and a program code for adding or subtracting for a transmission signal to be transmitted to the gateway station, a transmission signal to be transmitted to the other gateway station that is multiplied by the weight corresponding to the other gateway station, with respect to each of the plural gateway stations.

A program according to yet another aspect of the present invention is a program executed by a computer or a processor installed in a relay communication station that is incorporated in an aerial-staying type communication relay apparatus and relays radio communication of a terminal apparatus. The program comprises a program code for transmitting a plurality of spread pilot signals that are spectrally spread with a plurality of transmission-side spreading codes orthogonal to each other, to plural gateway stations that are time-synchronized with each other, a program code for receiving reception results of a plurality of inverse-spread pilot signals that are spectrally inverse-spread with a reception-side spreading code corresponding to the transmission-side spreading code by the plural gateway stations, a program code for estimating plural propagation path responses between the gateway stations and an antenna for feeder link of the communication relay apparatus in a transmission signal band of a feeder link, based on the reception results of the plurality of inverse-spread pilot signals, a program code for calculating a weight for suppressing an interference signal that causes an interference by a transmission signal transmitted from the relay communication station to the gateway station and received by another gateway station, based on the estimation results of the plural propagation path responses, with respect to each of the plural gateway stations, and a program code for adding or subtracting, for a transmission signal to be transmitted to the gateway station, a transmission signal to be transmitted to the other gateway station that is multiplied by the weight corresponding to the other gateway station, with respect to each of the plural gateway stations.

A program according to yet another aspect of the present invention is a program executed by a computer or a processor installed in a relay communication station that is incorporated in an aerial-staying type communication relay apparatus and relays radio communication of a terminal apparatus. The program comprises a program code for transmitting a plurality of spread pilot signals that are spectrally spread with a plurality of transmission-side spreading codes orthogonal to each other, to plural gateway stations that are time-synchronized with each other, a program code for receiving a calculation result of weight for suppressing an interference signal that causes an interference by a transmission signal transmitted from the relay communication station to the gateway station and received by another gateway station, wherein the calculation result is calculated by any one of the plural gateway stations or a common apparatus common to each gateway station based on reception results of a plurality of inverse-spread pilot signals that are spectrally inverse-spread with a reception-side spreading code corresponding to the transmission-side spreading code, with respect to each of the plural gateway stations, and a program code for adding or subtracting for a transmission signal to be transmitted to the gateway station, a transmission signal to be transmitted to the other gateway station that is multiplied by the weight corresponding to the other gateway station, with respect to each of the plural gateway stations.

A program according to yet another aspect of the present invention is a program executed by a computer or a processor installed in a relay communication station that is incorporated in an aerial-staying type communication relay apparatus and relays radio communication of a terminal apparatus. The program comprises a program code for receiving a spread pilot signal that is spectrally spread by each of plural gateway stations with a transmission-side spreading code different from each other, from plural gateway stations that are time-synchronized with each other, a program code for spectrally inverse-spreading the plurality of spread pilot signals with a reception-side spreading code corresponding to the transmission-side spreading code, a program code for estimating plural propagation path responses between the plural gateway stations and an antenna for feeder link of the communication relay apparatus in a transmission signal band of a feeder link, based on reception results of the plurality of inverse-spread pilot signals that are spectrally inverse-spread, a program code for calculating a weight for suppressing an interference signal that causes an interference by a transmission signal transmitted from the relay communication station to the gateway station and received by another gateway station, based on the plural propagation path responses, with respect to each of the plural gateway stations, and a program code for adding or subtracting for a transmission signal to be transmitted to the gateway station, a transmission signal to be transmitted to the other gateway station that is multiplied by the weight corresponding to the other gateway station, with respect to each of the plural gateway stations.

A program according to yet another aspect of the present invention is a program executed by a computer or a processor installed in a gateway station that transmits and receives relay signals different from each other on a same frequency in a feeder link to and from a relay communication station that is incorporated in an aerial-staying type communication relay apparatus and relays radio communication of a terminal apparatus. The program comprises a program code for time synchronizing with another gateway station that transmits and receives relay signals on the same frequency in the feeder link to and from the relay communication station, a program code for receiving a plurality of spread pilot signals that are spectrally spread with a plurality of transmission-side spreading codes orthogonal to each other, from the relay communication station, a program code for inverse-spreading by spectrally inverse-spreading reception signals of the spread pilot signals with a reception-side spreading code corresponding to the transmission-side spreading code, a program code for receiving reception results of a plurality of inverse-spread pilot signals from the other gateway station, wherein the other gateway station receives the plurality of spread pilot signals and spectrally inverse-spreads the plurality of spread pilot signals with a reception-side spreading code corresponding to the transmission-side spreading code, and a program code for estimating plural propagation path responses between own gateway station and the other gateway station and an antenna for feeder link of the communication relay apparatus in a transmission signal band of the feeder link, based on the reception results of the plurality of inverse-spread pilot signals of the own gateway station and the other gateway station, and transmitting the estimation result of the propagation path response to the relay communication station.

A program according to yet another aspect of the present invention is a program executed by a computer or a processor installed in a relay communication station that is incorporated in an aerial-staying type communication relay apparatus and relays radio communication of a terminal apparatus. The program comprises a program code for time synchronizing with another gateway station that transmits and receives relay signals on the same frequency in the feeder link to and from the relay communication station, a program code for receiving a plurality of spread pilot signals that are spectrally spread with a plurality of transmission-side spreading codes orthogonal to each other, from the relay communication station, a program code for inverse-spreading by spectrally inverse-spreading reception signals of the spread pilot signals with a reception-side spreading code corresponding to the transmission-side spreading code, a program code for receiving reception results of the plurality of inverse-spread pilot signals from the other gateway station, wherein the other gateway station receives the plurality of spread pilot signals and spectrally inverse-spreads with a reception-side spreading code corresponding to the transmission-side spreading code, a program code for estimating plural propagation path responses between own gateway station and the other gateway station and an antenna for feeder link of the communication relay apparatus in a transmission signal band of the feeder link based on the reception results of the plurality of inverse-spread pilot signals of the own gateway station and the other gateway station, and a program code for calculating a weight for suppressing an interference signal that causes an interference by a transmission signal transmitted from the relay communication station to the gateway station and received by another gateway station, based on the estimation results of the plural propagation path responses, with respect to each of the plural gateway stations.

A program according to yet another aspect of the present invention is a program executed by a computer or a processor installed in a gateway station that transmits and receives relay signals different from each other on a same frequency in a feeder link to and from a relay communication station that is incorporated in an aerial-staying type communication relay apparatus and relays radio communication of a terminal apparatus. The program comprises a program code for time synchronizing with another gateway station that transmits and receives relay signals on the same frequency in the feeder link to and from the relay communication station, a program code for receiving a plurality of spread pilot signals that are spectrally spread with a plurality of transmission-side spreading codes orthogonal to each other, from the relay communication station, a program code for receiving a reception result of the other gateway station receiving the spread pilot signal transmitted from the relay communication station, from the other gateway station, a program code for inverse-spreading by spectrally inverse-spreading reception signals of the spread pilot signals with a reception-side spreading code corresponding to the transmission-side spreading code, a program code for receiving reception results of the plurality of inverse-spread pilot signals from the other gateway station, wherein the other gateway station receives the plurality of spread pilot signals and spectrally inverse-spreads with a reception-side spreading code corresponding to the transmission-side spreading code, a program code for estimating plural propagation path responses between own gateway station and the other gateway station and an antenna for feeder link of the communication relay apparatus in a transmission signal band of the feeder link based on the reception results of the plurality of inverse-spread pilot signals of the own gateway station and the other gateway station, a program code for calculating a weight for suppressing an interference signal that causes an interference by a transmission signal transmitted from the relay communication station to the own gateway station and received by another gateway station, based on the plural propagation path responses, and a program code for adding or subtracting, for a reception signal received by the own station, a reception signal received by the other gateway station that is multiplied by the weight corresponding to the other gateway station.

In the foregoing system, the foregoing relay communication station, the foregoing aerial-staying type communication relay apparatus, the foregoing gateway station, the foregoing interference suppression method and the foregoing program, the plurality of spreading codes may be orthogonal to each other, and the plurality of pilot signals may be transmitted and received at the same frequency.

The plurality of pilot signals may be transmitted and received by being distributed in plural guard bands located on both sides of the transmission signal band of the feeder link.

The plurality of pilot signals may be transmitted and received within the transmission signal band of the feeder link.

Moreover, at the center frequency of the transmission signal band of the feeder link or a frequency around the center frequency, the plural weights may be calculated by estimating the plural propagation path responses.

Further, each of the plural weights may be calculated by the ZF (Zero-Forcing) method or the MMSE (Minimum Mean Square Error) method using matrix of the propagation path response.

Each of the plural gateway stations may comprise an antenna control section that controls an antenna for feeder link so as to track the aerial-staying type communication relay apparatus.

The aerial-staying type communication relay apparatus may comprise an antenna for feeder link having plural directional beams respectively corresponding to the plural gateway stations, and an antenna control section for controlling the antenna for feeder link so that each of the plural beams directs toward a corresponding gateway station.

The antenna for feeder link may be plural feeder link antennas having directional beams in directions different from each other, and the antenna control section may mechanically control each of the plural antennas for feeder link so that the directional beams of the plural antennas for feeder link are directed toward the corresponding gateway stations.

The antenna for feeder link may be an array antenna capable of forming the plural directional beams in an arbitrary outward direction centered on a virtual axis in the vertical direction, and the antenna control section may control amplitudes and phases of transmission and reception signals with respect to plural antenna elements of the array antenna so that each of the plural directional beams is directed toward the corresponding gateway station.

The antenna for feeder link may be plural array antennas capable of forming a directional beam in a predetermined angle range centered on directions different from each other, and the antenna control section may selectively perform a control of amplitudes and phases of transmission and reception signals with respect to plural antenna elements of each array antenna and a switching control of the plural array antennas so that each of the plural directional beams of the plural array antennas is directed toward the corresponding gateway station.

Advantageous Effects of Invention

According to the present invention, since it is not necessary to use narrowband pilot signals as a plurality of pilot signals used for dynamic suppression of an interference in a multi-feeder link of a same frequency between an aerial-floating type communication relay apparatus and plural gateway stations, there is no need to provide a highly stable oscillation frequency circuit for transmitting narrowband pilot signals on a transmission-side, and a narrowband reception filter that separates narrowband pilot signals on a reception-side becomes unnecessary. Therefore, it is possible to realize dynamic suppression of the interference in the multi-feeder link between the aerial-floating type communication relay apparatus and the plural gateway stations with a simple configuration.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an illustration showing an example of a HAPS cell configuration in a communication system according to an embodiment of the present invention.

FIG. 2A is a side view showing an example of a schematic configuration of plural GW systems according to an embodiment.

FIG. 2B is a top view illustration of a relationship between plural antennas for feeder link of a HAPS and plural GW stations.

FIG. 3 is an illustration showing an example of state in which GW antennas of plural GW stations are tracking a HAPS according to an embodiment.

FIG. 4 is an illustration showing an example of directional beams of plural FL antennas of a HAPS according to an embodiment.

FIG. 5 is an illustration showing an example of a directional beam control of FL antennas in a HAPS according to an embodiment.

FIG. 6 is an illustration showing another example of a directional beam control of FL antennas in a HAPS according to an embodiment.

FIG. 7 is an illustration showing yet another example of a directional beam control of FL antennas in a HAPS according to an embodiment.

FIG. 8 is an illustration of an example of a forward link interference between GW stations (between feeder links) in plural GW systems.

FIG. 9 is an illustration of an example of a reverse link interference between GW stations (between feeder links) in plural GW systems.

FIG. 10 is an illustration showing an example of a MIMO interference canceller to which a weight W is obtained by an approximate expression and applied.

FIG. 11 is an illustration showing an example of a schematic configuration of an interference canceller section of a forward link provided on a HAPS side (reception-side) in a multi-feeder link of plural GW systems according to an embodiment.

FIG. 12 is an illustration showing an example of a MIMO interference canceller applied by obtaining a weight W by the ZF method.

FIG. 13 is an illustration showing an example of narrowband pilot signals in a transmission signal band of an uplink transmitted from each GW station.

FIG. 14 is an illustration showing an example of narrowband pilot signals in a reception signal band of an uplink received by a HAPS.

FIG. 15 is an illustration showing an example of narrowband pilot signals used for deriving a propagation path response.

FIG. 16 is an illustration showing an example of a derivation model of a propagation path response of a feeder link.

FIG. 17 is an illustration showing an example of spread-spectrum pilot signals in a transmission signal band of an uplink transmitted from a GW station according to an embodiment.

FIG. 18 is an illustration showing an example of spread-spectrum pilot signals in a reception signal band of an uplink received by a HAPS according to an embodiment.

FIG. 19 is an illustration showing an example of pilot signal groups before inverse-spreading that are received by a HAPS and separated by a filter according to an embodiment.

FIG. 20 is an illustration showing an example of pilot signal groups after inverse-spreading according to an embodiment.

FIG. 21A is a functional block diagram showing an example of a transmitter of a GW station.

FIG. 21B is a spectrum diagram showing an example of a desired signal (S_(i)) and a spread pilot signal (C_(i)S_(P1)) that is spectrally spread in a transmission signal transmitted from a transmitter of a GW station.

FIG. 22A is a functional block diagram showing an example of a receiver of a relay communication station of a HAPS.

FIG. 22B is a spectrum diagram showing an example of a desired signal (S_(i)) and a spread pilot signal (C_(i)S_(P1)) that is spectrally spread in a reception signal received by a receiver of a relay communication station of a HAPS.

FIG. 23 is an illustration showing an example of a main configuration of a relay communication station of a HAPS according to an embodiment.

FIG. 24 is an illustration showing another example of spread-spectrum pilot signals in a transmission signal band of an uplink transmitted from a GW station according to an embodiment.

FIG. 25A is an illustration showing an example of a schematic configuration of an interference canceller section of a reverse link, which is provided on a GW station side (reception-side) in a multi-feeder link of plural GW systems according to another embodiment.

FIG. 25B is an illustration showing a relationship between a transmission signal S and a reception signal Y.

FIG. 26A is an illustration showing an example of a schematic configuration of an interference canceller section of a reverse link provided on a HAPS 20 side (transmission-side) in a multi-feeder link of plural GW systems according to yet another embodiment.

FIG. 26B is an illustration showing a relationship between a transmission signal S and a reception signal Y.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention are described with reference to the drawings.

FIG. 1 is an illustration showing an example of a cell configuration of a HAPS 20 in a communication system according to an embodiment of the present invention. The communication system according to the present embodiment is suitable for realizing a three-dimensional network of the fifth-generation or the later generation mobile communication that supports simultaneous connection to a large number of terminal apparatuses, and low delay, etc. The mobile communication standards disclosed in the present specification are applicable to communication systems, radio relay stations, base stations, repeaters and terminal apparatuses include the fifth-generation mobile communication standard and the fifth-generation and subsequent generation mobile communication standards.

As shown in FIG. 1 , the communication system is provided with High-Altitude Platform Stations (HAPS) (also called “high altitude pseudo satellite” or “stratified platform”) 20 as plural aerial-floating type communication relay apparatuses (radio relay apparatuses). The HAPS 20 is located in an airspace at a predetermined altitude, and forms three-dimensional cell (three-dimensional area) in a cell-formation target airspace at a predetermined altitude. The HAPS 20 is an airship as a floating object that is controlled by autonomous control or external control so as to float or fly and be located in an airspace (floating airspace) with high altitude of 100 [km] or less from the ground level or the sea level, and a relay communication station 21 is mounted on the airship.

The airspace in which the HAPS 20 is located is, for example, a stratospheric airspace with altitude greater than 11 [km] and less than 50 [km] on the ground (or on the water such as the sea or lake). The airspace may be an airspace in an altitude of 15 [km] or more and 25 [km] or less where weather conditions are relatively stable, and may be an airspace with altitude of about 20 [km] in particular.

The cell-formation target airspace, which is a target airspace for forming a three-dimensional cell with one or two or more HAPSs according to the communication system in the present embodiment, is an airspace in a predetermined altitude range (for example, altitude range of 50 [m] or more and 1000 [m] or less) located between the airspace where the HAPS 20 is located and a cell-formation spatial area near the ground level covered by a base station (for example, LTE eNodeB) such as a conventional macro-cell base station.

It is noted that, the cell-formation target airspace where the three-dimensional cell in the present embodiment is formed may be an airspace over the sea, a river or a lake. Further, the three-dimensional cell formed by the HAPS 20 may be formed so as to reach the ground level or the sea level so that it can communicate with a terminal apparatus 61 located on the ground or on the sea.

The relay communication stations of the HAPS 20 respectively form plural beams for wirelessly communicating with the terminal apparatus 61 that is a mobile station, toward the ground by an antenna for service link (hereinafter referred to as “SL antenna”) 215. The terminal apparatus 61 may be a communication terminal module incorporated in a drone that is an aircraft such as a small helicopter capable of remotely steering, or may be a user apparatus used by a user in an airplane. An area through which the beam passes in the cell-formation target airspace is a three-dimensional cell. The plural beams adjacent to each other in the cell-formation target airspace may be partially overlapped with each other.

Each of the relay communication stations 21 of the HAPSs 20 is, for example, a base station that wirelessly communicates with a gateway station (also referred to as a “feeder station”) 70 as a relay station connected to a core network on the ground (or on the sea) side, or a slave repeater that wirelessly communicates with the feeder station (master repeater) 70 as a relay station connected to a base station on the ground (or on the sea) side.

The relay communication station 21 of the HAPS 20 is connected to a core network of a mobile communication network 80 via the feeder station 70, which is installed on the ground or on the sea, capable of radio communication by an antenna for feeder link (hereinafter referred to as “FL antenna”) 211. A communication of feeder link between the HAPS 20 and the feeder station 70 may be performed by a radio communication using a radio wave such as a microwave or a millimeter wave, or may be performed by an optical communication using a laser light or the like.

Each of the HAPS 20 may autonomously control its own floating movement (flight) and a process in the relay communication station 21 by executing a control program with a control section including a computer or the like incorporated inside of the HAPS. For example, each of the HAPS 20 may acquire its own current position information (for example, GPS position information), position control information (for example, flight schedule information) stored in advance, position information on another HAPS located in a peripheral space or the like, and may autonomously control floating movement (flight) and process in the relay communication station 21 based on these pieces of information.

Further, the floating movement (flight) of each of the HAPS 20 and the process in the relay communication station 21 may be controlled by a management apparatus (also referred to as a “remote control apparatus”) as a management apparatus provided in a communication center or the like of the mobile communication network. The management apparatus can be configured with, for example, a computer apparatus such as a PC, a server, or the like. In this case, the HAPS 20 may incorporate a communication terminal apparatus for control (for example, mobile communication module) so that it can receive control information from the management apparatus and transmit various pieces of information such as monitoring information to the management apparatus, and may be assigned terminal identification information (for example, IP address, phone number, etc.) so that it can be identified from the management apparatus. The MAC address of the communication interface may be used to identify the communication terminal apparatus for control.

Moreover, each of the HAPS 20 may transmit information regarding the floating movement (flight) of the own HAPS or a surrounding HAPS and/or the process at the relay communication station 21, and monitoring information such as information on statuses of the HAPS 20 and observation data acquired by various kinds of sensors, to a predetermined destination such as the management apparatus. The control information may include information on target flight route of the HAPS. The monitoring information may include at least one of information on current positions, flight-route history information, velocity relative to the air, velocity relative to the ground and propulsion direction of the HAPS 20, wind velocity and wind direction around the HAPS 20, and atmospheric pressure and temperature around the HAPS 20.

Duplex methods of uplink and downlink for radio communication with the relay communication station 21 and the terminal apparatus 61 are not limited to specific methods, and may be, for example, a time division duplex method (Time Division Duplex: TDD) or a frequency division duplex method (Frequency Division Duplex: FDD). An access method for radio communication with the relay communication station 21 and the terminal apparatus 61 is not limited to the specific method, but may be, for example, FDMA (Frequency Division Multiple Access) method, TDMA (Time Division Multiple Access) method, CDMA (Code Division Multiple Access) method, or OFDMA (Orthogonal Frequency Division Multiple Access). In the foregoing radio communication, a MIMO (Multi-Input and Multi-Output) technology may be used, which has functions of diversity/coding, transmission beam forming, spatial division multiplexing (SDM: Spatial Division Multiplexing), etc., and in which a transmission capacity per unit frequency can be increased by simultaneously using plural antennas for both of transmission and reception. The MIMO technology may be an SU-MIMO (Single-User MIMO) technology in which one base station transmits plural signals to one terminal apparatus on the same time/same frequency, and may be an MU-MIMO (Multi-User MIMO) technology in which one base station transmits signals to plural communication terminal apparatuses different from each other on the same time/same frequency or plural different base stations transmit signals to one terminal apparatus on the same time/same frequency.

It is noted that, in the following embodiments, although it is illustrated and described regarding some cases in which a communication relay apparatus having the relay communication station 21 that wirelessly communicates with the terminal apparatus 61 is an unmanned-airship type HAPS 20, the communication relay apparatus may be a solar-plane type HAPS. Further, the following embodiments can be similarly applied to aerial-floating type communication relay apparatuses other than the HAPS.

A link between the HAPS 20 and a base station 90 via a gateway station (hereinafter abbreviated as “GW station”) 70 as a feeder station is referred to as a “feeder link”, and a link between the HAPS 10 and the terminal apparatus 61 is referred to as a “service link”. In particular, a spatial section between the HAPS 20 and the GW station 70 is referred to as a “radio section of feeder link”. Further, a downlink of a communication from the GW station 70 to the terminal apparatus 61 via the HAPS 20 is referred to as a “forward link”, and an uplink of a communication from the terminal apparatus 61 to the GW station 70 via the HAPS 20 is also referred to as a “reverse link”.

In FIG. 1 , although the communication relay apparatus is the unmanned-airship type HAPS 20, it may be a solar-plane type HAPS. Further, in the illustrated example, although the HAPS 20 is located in the stratosphere with an altitude of about 20 km, the HAPS 20 forms plural cells 200C(1) to 200C(7), and a diameter of a service area 20A consisting of footprints 200F(1) to 200F(7) of the cells 200C(1) to 200C(7) of the plural cells (7 cells) configuration is 100 to 200 km, it is not limited to these examples.

In FIG. 1 , a communication service that directly communicates with the terminal apparatus 61 on the ground (or on the water) using the HAPS 20 located in the stratosphere is very attractive as an expansion of service area and a communication means in the event of a disaster. The communication line of the HAPS 20 comprises a feeder link FL connecting the GW station 70 and the HAPS 20, and a service link SL connecting the HAPS 20 and the terminal apparatus 61. Since the communication capacity of the service link depends on the communication capacity of the feeder link which is the relay frequency, it is necessary to improve the frequency utilization efficiency of the feeder link. In particular, in case that the service link has a multi-cell configuration as shown in FIG. 1 , the communication capacity of the feeder link tends to be insufficient, so that a frequency effective utilization technology for the feeder link is indispensable. However, in case that the HAPS 20 and the GW station 70 are configured one-to-one, it is difficult to improve the frequency utilization efficiency of the feeder link.

Therefore, in the present embodiment, a plural-gateway system (hereinafter also referred to as “plural-GW system”) is constructed, which is configured with plural GW stations that transmit and receive relay signals different from each other on a same frequency to and from the HAPS 20 in the feeder links of Frequency Division Duplex (FDD) method, and performs a spatial-division multiplex communication in a multi feeder link formed between one HAPS 20 and plural GW stations. In the plural-GW system, by eliminating interference between the plural feeder links, the frequency utilization efficiency can be improved depending on the number of GW stations to be installed.

It is noted that, in the following embodiments, although it is described regarding some cases in which the spatial-division multiplex communication between the HAPS 20 and the plural GW stations is performed only by a forward link of the feeder link, the spatial-division multiplex communication may be performed only by a reverse link of the feeder link, or may be performed by both of the forward link and the reverse link.

FIG. 2A is a side view showing an example of a schematic configuration of plural GW systems according to the embodiment, and FIG. 2B is a top view illustration of a relationship between plural FL antennas 211(1) to 211(3) of the HAPS 20 and plural GW stations 70(1) to 70(3). In the illustrated example, each of the number of FL antennas (N) and the number of GW stations (N) is the same number (3 in the illustrated example), and the same number of FL antennas 211(1) to 211(3) and GW stations 70(1) to 70(3) are provided in a one-to-one correspondence with each other. The number of sets of the FL antenna 211 and the GW station 70 may be two sets, or may be four or more sets. Further, in the illustrated example, although the plural GW stations 70 are disposed so that distances from the HAPS 20 and intervals between the GW stations are equal to each other, at least one of the distances and the intervals may be different from each other. Each GW station 70 is disposed so that complex amplitudes received by each FL antenna 211 (also referred to as “HAPS station antenna”) of the HAPS 20 are uncorrelated. Further, the antennas for feeder link (hereinafter referred to as “GW antennas”) 71(1) to 71(3) of the GW stations 70(1) to 70(3) can transmit and receive radio signals with two kinds of polarized waves of vertically polarized waves (V) and horizontally polarized waves (H) which are orthogonal to each other. In the illustrated example, although the plural FL antennas 211(1) to 211(3) of the HAPS 20 are disposed so that distances from the center of the HAPS 20 and intervals between the FL antennas are equal to each other, at least one of the distances and the intervals may be different from each other between the FL antennas. For example, the distances and the intervals may be different from each other between the FL antennas.

As shown in FIG. 3 , each of the plural GW stations 70(1) to 70(3) may be provided with an antenna control section that controls the GW antennas 71(1) to 71(3) so as to track the HAPS 20 moving in an airspace. A HAPS 20′ with dashed line in the figure indicates a position before the movement, and a solid line HAPS 20 in the figure indicates a position after the movement. By tracking the HAPS 20 by each of the GW antennas 71(1) to 71(3), even when using the GW antennas 71(1) to 71(3) with high directivity such as a parabolic antenna, it is capable of suppressing the deterioration of the communication quality of the feeder link due to the movement of the HAPS 20.

As shown in FIG. 4 , the plural FL antennas 211(1) to 211(3) of the HAPS 20 may include antenna directional beams (hereinafter referred to as “directional beams” or “beams”) 212(1) to 212(3) respectively corresponding to the GW stations 70(1) to 70(3), and the HAPS 20 may be provided with an antenna control section that controls the FL antennas 211(1) to 211(3) so that the directional beams 212(1) to 212(3) of the plural FL antennas 211(1) to 211(3) is respectively directed in the direction of the corresponding GW stations 70(1) to 70(3). Each of the directional beams 212(1) to 212(3) of the FL antennas 211(1) to 211(3) is formed, for example, so as to face the GW station 70 closest to itself and not to provide an interference to other GW stations, that is, so that a ratio (F/B) of a gain of the main beam and a gain in the opposite direction becomes sufficiently large. As a result, even when the HAPS 20 moves or rotates, it is possible to suppress the deterioration of the communication quality of the feeder link due to the movement and rotation of the HAPS 20.

As a control system of the directional beams 212(1) to 212(3) of the plural FL antennas 211(1) to 211(3) by the antenna control section of the HAPS 20, it is capable of using various systems such as a gimbal system, an electric system (360-degrees beamforming control system), and an electric system (angle-limited beamforming control system+antenna switching).

For example, in the gimbal system in FIG. 5 , in accordance with the rotation (turning) around the vertical axis (yawing axis, Z axis) of the HAPS 20, the rotation drive of the whole of plural FL antennas 211(1) to 211(3) can be mechanically controlled around the foregoing axis. For example, in FIG. 5 , when the HAPS 20 rotates about 45 degrees in the left direction of rotation (counterclockwise direction) Rb, the rotation of the whole of plural FL antennas 211(1) to 211(3) are mechanically driven in the right direction of rotation (clockwise direction) Ra opposite to the foregoing direction of rotation of the HAPS20.

Although the rotational drive control for angle adjustment of each of the FL antennas 211(1) to 211(3) may be performed with reference to information on a position and an orientation of the HAPS, the rotational drive control of respective FL antenna 211(1) to 211(3) may be performed with reference to reception level values of the FL antennas 211(1) to 211(3). For example, each of the FL antennas 211(1) to 211(3) is rotated in small steps, an angle for maximizing the reception level of each of the FL antennas 211(1) to 211(3) is found, and the rotational drive control of each of the FL antennas 211(1) to 211(3) is performed so as to face the angle. Herein, a threshold value may be set for each of the reception levels of each of the FL antennas 211(1) to 211(3), each of the FL antennas 211(1) to 211(3) may be rotated by a predetermined angle when the reception level falls below the foregoing threshold, and the rotational drive control of the FL antennas 211(1) to 211(3) may be performed to the directional angle at which the reception level is maximized. The threshold value of the reception level may be obtained, for example, by an experiment in advance, and the predetermined angle may be, for example, 360 degrees/number of FL antennas (120 degrees in the illustrated example). Further, a monitoring beam for comparing the reception level from the GW stations other than the corresponding GW station may be generated from the FL antenna 211(1) to 211(3), a GW station having the maximum level may be selected, and the rotational drive of each of the FL antennas 211(1) to 211(3) may be controlled so that the directional beam is directed in the direction to the selected GW station.

It is noted that, although the angle adjustment in the horizontal direction of each of the FL antennas 211(1) to 211(3) is shown in FIG. 5 , the angle adjustment in the vertical direction may be also performed in the same manner.

By the rotational drive control of the FL antennas 211(1) to 211(3), even if the HAPS 20 rotates, since the directional beams 212(1) to 212(3) of the FL antennas 211(1) to 211(3) are directed in the corresponding directions of the GW stations 70(1) to 70(3) respectively, the deterioration of the communication quality of the feeder link can be prevented.

In the electric system (360-degrees beamforming control system) of FIG. 6 , a circular array antenna 213 in which plural antenna elements 213 a are disposed along the circumferential shape is provided as a FL antenna. Based on information on a position and an attitude of the HAPS 20, a weight applied to signals (amplitude, phase) transmitted and received via each of the plural antenna elements 213 a is controlled. For example, the information on the position and the attitude of the HAPS 20 may be acquired based on an output of a GNSS Inertial Navigation System (GNSS/INS) that is a combination of a GNSS (Global Navigation Satellite System) system and an Inertial Measurement Unit (IMU) incorporated in the HAPS 20.

Although the weight control of each antenna element 213 a of the circular array antenna 213 may be performed with reference to the information on the position and the attitude of the HAPS, the weight control of each antenna element 213 a may be performed so as to form a directional beam having the maximum reception level at a directional position corresponding to each GW station with reference to the reception level value of each antenna element 213 a of the circular array antenna 213. For example, a phase of each antenna element 213 a of the circular array antenna 213 is changed in small steps, an angle for maximizing the reception level is found, and the weight control of each antenna element 213 a is performed so that a beam is formed in the direction of the found angle. Further, a monitoring beam for comparing the reception level from the GW stations other than the corresponding GW station may be generated from the circular array antenna 213, a GW station having the maximum level may be selected, and a beam may be formed in the direction to the selected GW station.

It is noted that, although the beam angle adjustment in the horizontal direction is shown in FIG. 6 , the beam angle adjustment may be also performed in the same manner in the vertical direction.

By controlling the weight of each antenna element 213 a of the circular array antenna 213, the directional beams 212(1) to 212(3) respectively directed in the directions to the plural GW stations 70(1) to 70(3) are formed. As a result, even if the HAPS 20 rotates, since the directional beams 212(1) to 212(3) of the FL antennas 211(1) to 211(3) are directed in the corresponding directions to the GW stations 70(1) to 70(3) respectively, the deterioration of the communication quality of the feeder link can be prevented.

In the electric system (beamforming control system with limited angle+antenna switching) of FIG. 7 , plural planar array antennas 214(1) to 214(3) in which plural antenna elements 214 a of each array antenna are two-dimensionally disposed in a plane are provided as a FL antenna. Based on information on the position and the attitude of the HAPS 20 acquired by GNSS/INS etc., a beamforming control is performed to control a weight applied to a signal (amplitude, phase) transmitted and received via each of the plural antenna elements 214 a of the plural planar array antennas 214(1) to 214(3).

Although the control of the switching and the beamforming of the planar array antennas 214(1) to 214(3) may be performed with reference to the information on the position and the attitude of the HAPS, the antenna switching and beamforming may be controlled so that each of the planar array antennas 214(1) to 214(3) has the maximum reception level with reference to the reception level value of each of the planar array antennas 214(1) to 214(3). For example, each of the planar array antennas 214 (1) to 214 (3) is rotated in small steps, an angle for maximizing the reception level of respective planar array antennas 214(1) to 214(3) is found, and the rotational drive control of each antenna is performed so as to be directed to the found angle. Herein, a threshold value may be set for each of the reception levels of each of the planar array antennas 214(1) to 214(3), when the reception level falls below the foregoing threshold value, the planar array antennas 214(1) to 214(3) may be switched and each of the planar array antennas 214(1) to 214(3) may be rotated by a predetermined angle, and a beamforming may be performed to form a beam to the directional angle at which the reception level is maximized. The threshold value of the reception level may be obtained, for example, by an experiment in advance, and the predetermined angle may be, for example, 360 degrees/number of FL antennas (120 degrees in the illustrated example). Further, a monitoring beam for comparing the reception level from the GW stations other than the corresponding GW station may be generated from the planar array antenna 214(1) to 214(3), a GW station, for which each of the planar array antennas 214(1) to 214(3) has the maximum level, may be selected, and an antenna switching and a beamforming may be performed so as to form a beam in the direction to the selected GW station.

It is noted that, although the beam angle adjustment in the horizontal direction is shown in FIG. 7 , the beam angle adjustment may be also performed in the same manner in the vertical direction.

By controlling the switching and the beamforming of the planar array antennas 214(1) to 214(3), the directional beams 212(1) to 212(3) respectively directed in the directions to the plural GW stations 70(1) to 70(3) are formed. Herein, for example, when the angle (θ in the figure) at which the directional beam 212(1) is tilted with respect to the normal direction perpendicular to the plane of the planar array antenna 214(1) becomes larger than the preset predetermined angle θth degrees, the FL antenna corresponding to the GW station 70(1) is switched to the planar array antenna 214(2). As a result, even if the HAPS 20 rotates, each of the directional beams 212(1) to 212(3) of the FL antennas 211(1) to 211(3) are directed in the directions to the corresponding GW stations 70(1) to 70(3), so that the deterioration of the communication quality of the feeder link can be prevented.

In the plural GW systems with the above-described configuration, an interference in at least one of the forward link and the reverse link between the GW stations (between feeder links) may increase. For example, as shown in FIG. 8 , while a desired signal (desired signal) S1 transmitted from the GW station 70(1) is received by the FL antenna 211(1) of the HAPS 20, signals transmitted from other GW stations 70(2) and 70(3) are received by the FL antenna 211(1) as interference signals I2 and I3. Therefore, SINR characteristics of the feeder link may deteriorate. As shown in FIG. 9 , when the desired signal (desired signal) S1 transmitted from the FL antenna 211(1) of the HAPS 20 is receiving by the GW station 70(1), signals transmitted from the other FL antennas 211(2) and 211(3) of the HAPS 20 are received as interference signals I2 and I3 by the GW station 70(1). Accordingly, the SINR characteristics of the feeder link (reverse link) may deteriorate.

Therefore, in the present embodiment, by applying a MIMO interference canceller supporting the line-of-sight environment (LOS: Line-Of-Sight) between the GW stations (between the feeder links) as shown below, and by reducing an interference of forward link and reverse link between the GW stations (between the feeder links), the SINR characteristics of the feeder links (forward and reverse links) are improved.

First, a configuration and a method for reducing an interference of the forward link between the GW stations (between the feeder links) in the plural GW systems of the present embodiment are described.

[MIMO Interference Canceller (Reception Interference Canceller) of Forward Link on HAPS Side (Transmission-Side)]

FIG. 10 is an illustration showing an example of a MIMO interference canceller to which a weight W is obtained by an approximate expression and applied. FIG. 11 is an illustration showing an example of a schematic configuration of an interference canceller section 220 of a forward link provided on a HAPS side (transmission-side) in a multi-feeder link of plural GW systems according to an embodiment. The FL antenna 211(1) of the HAPS 20 receives a desired signal S1(Y11) transmitted from the GW station 70(1), an interference signal I2(Y12) transmitted from the GW station 70(2), and an interference signal I3(Y13) transmitted from the GW station 70(3). The reception signal AN1 is represented by the following equation (1). AN1=S1+I2+I3  (1)

In the interference canceller section 220 of the HAPS 20, as shown in the following equation (2), by multiplying the signals S2 and S3 received by the other FL antennas 211(2) and 211(3) by the weights W2 and W3 respectively corresponding to the signals and subtracting them, the desired signal S1(Y11) in which the interference signals I2 and I3 are canceled can be output. Similarly, for desired signals S2(Y22) and S3(Y33) transmitted from the GW stations 70(2) and 70(3), interference signals from other GW stations can be canceled. S1=w11·AN1+w12·AN2+w13·AN3  (2)

FIG. 12 is an illustration showing an example of a MIMO interference canceller applied by obtaining a weight W by the ZF (Zero-Forcing) method. For example, the signal transmitted from the GW station 70(1) is not only received by the FL antenna 211(1) of the HAPS 20 as the desired signal S1(Y11), but also received by the FL antennas 211(2) and 211(3) as the interference signals I1(Y12) and I1′(Y13). The signal transmitted from the GW station 70(2) is not only received by the FL antenna 211(1) as an interference signal I2(Y21), but also received by the FL antenna 211(3) as an interference signal I2′(Y23). Further, the signal transmitted from the GW station 70(3) is not only received by the FL antenna 211(1) as an interference signal I3(Y31), but also received by the FL antenna 211(2) as an interference signal I3′(Y32). In the MIMO interference canceller of FIG. 12 , considering these interference signals I1, I1′, I2′ and I3′, for example, the desired signal S1(Y11) is output as shown in the following equation (3). S1=w11(Y11+Y12+Y13)+w12(Y21+Y22+Y23)+w13(Y31+Y32+Y33)   (3)

In order to calculate the weight W used for the MIMO interference canceller, it is necessary to grasp a propagation path response H between the FL antennas 211(1) to 211(3) of the HAPS 20. In particular, in the plural GW systems of the present embodiment, since an airship of the HAPS 20 moves relative to the GW stations 70(1) to 70(3), the propagation path response also changes according to the movement.

In the present embodiment, in order to dynamically grasp the propagation path response, pilot signals are transmitted from each of the GW stations 70(1) to 70(3).

FIG. 13 is an illustration showing an example of narrowband pilot signals in a transmission signal band of an uplink transmitted from the GW stations 70(1) to 70(3) according to a reference example. FIG. 14 is an illustration showing an example of narrowband pilot signals in a reception signal band of an uplink received by the HAPS 20 according to a reference example. FIG. 15 is an illustration showing an example of narrowband pilot signals that are separated by a filter and used for deriving a propagation path response according to a reference example. FIG. 16 is an illustration showing an example of a derivation model of a propagation path response of a feeder link using the pilot signals in FIG. 13 to FIG. 15 .

In the illustrated example, a plurality of pilot signals transmitted from each of the GW stations 70(1) to 70(3) are distributed and arranged, in each of a first guard band GB1 as a first adjacent band and a second guard band GB2 as a second adjacent band, wherein the first adjacent band and the second adjacent band are adjacent to the transmission signal band FB of the feeder link in which the desired signals S_(i), S2, S3 are transmitted from the GW stations 70(1) to 70(3), from the low frequency side and the high frequency side. Specifically, pilot signals S_(P1), S_(P2), and S_(P3) with frequencies f₁, f₂, and f₃ different from each other on the same frequency, which are respectively transmitted from the GW stations 70(1) to 70(3), are located in the first guard band GB1. Pilot signals S_(P1)′, S_(P2)′, S_(P3)′ with frequencies f₁′, f₂′, f₃′ different from each other, which are respectively transmitted from the GW stations 70(1) to 70(3), are located in the second guard band GB2. The relay communication station 21 of the HAPS 20 separates the plural pilot signals S_(P1), S_(P2), S_(P3) of the first guard band GB1 received from the GW stations 70(1), 70(2) and 70(3) by a filter, respectively, and separates the plural pilot signals S_(P1)′, S_(P2)′, S_(P3)′ Of the second guard band GB2 received from the GW stations 70(1), 70(2) and 70(3) by a filter, respectively.

Next, the relay communication station 21 of the HAPS 20 separates each of the pilot signals S_(Pi) (i=1 to 3) from the reception signal by using a narrowband reception filter 218 as shown in FIG. 14 (see FIG. 15 ), and obtains a propagation path response h_(ki) from k-th GW station 70(k) to the FL antenna 211(i) of i-th transmitter of the HAPS 20, from the separated pilot signals S_(Pi). The relay communication station 21 outputs information on the obtained propagation path response h_(ki) (see the following equations (4) and (5)) to the interference canceller section 220.

$\begin{matrix} {P_{ki} = {h_{ki}S_{pi}}} & (4) \end{matrix}$ $\begin{matrix} {h_{ki} = \frac{P_{ki}}{S_{pi}}} & (5) \end{matrix}$

For example, each of the pilot signals h₁₁, h₁₁′, h₂₁ and h₂₁′ received by the FL antennas 211(1) and 211(2) of the HAPS 20 is represented by the following equations (6), (7), (8) and (9), and each of the ratios / and / of these signals is represented by the following equations (10) and (11).

$\begin{matrix} {h_{11} = {{{❘h_{11}❘}e^{j\theta_{11}}} = {{❘h_{11}❘}e^{j2\pi f_{1}\frac{d_{1}}{c}}}}} & (6) \end{matrix}$ $\begin{matrix} {h_{11}^{\prime} = {{{❘h_{11}❘}e^{j\theta_{11}^{\prime}}} = {{❘h_{11}❘}e^{j2\pi f_{1}^{\prime}\frac{d_{1}}{c}}}}} & (7) \end{matrix}$ $\begin{matrix} {h_{21} = {{{❘h_{21}❘}e^{j\theta_{21}}} = {{❘h_{21}❘}e^{j2\pi f_{1}\frac{d_{1} + {\Delta d_{21}}}{c}}}}} & (8) \end{matrix}$ $\begin{matrix} {h_{21}^{\prime} = {{{❘h_{21}❘}e^{j\theta_{21}^{\prime}}} = {{❘h_{21}❘}e^{j2\pi f_{1}^{\prime}\frac{d_{1} + {\Delta d_{21}}}{c}}}}} & (9) \end{matrix}$ $\begin{matrix} {\frac{h_{21}}{h_{11}} = {{\frac{❘h_{21}❘}{❘h_{11}❘}e^{j({\theta_{21} - \theta_{11}})}} = {\frac{❘h_{21}❘}{❘h_{11}❘}e^{j2\pi f_{1}\frac{\Delta d_{21}}{c}}}}} & (10) \end{matrix}$ $\begin{matrix} {\frac{h_{21}^{\prime}}{h_{11}^{\prime}} = {{\frac{❘h_{21}❘}{❘h_{11}❘}e^{j({\theta_{21}^{\prime} - \theta_{11}^{\prime}})}} = {\frac{❘h_{21}❘}{❘h_{11}❘}e^{j2\pi f_{1}^{\prime}\frac{\Delta d_{21}}{c}}}}} & (11) \end{matrix}$

In the above equations (6) to (11), d₁ is a path length between the GW station 70(1) and the FL antenna 211(1), and Δd₂₁ is a difference in path length (path difference) between the GW station 70(1) and each of the FL antennas 211(1) and 211(2). A path length between the GW station 70(1) and the FL antenna 211(2) is represented by d₁+Δd₂₁.

From the foregoing equations (10) and (11), the path difference Δd₂₁ can be obtained by the following equation (12). Note that θ in the equation (12) is a phase difference obtained by adding a phase difference between h₁₁′ and h₁₁ and phase difference between h₂₁ and h₂₁′. That is, θ=(phase difference between h₁₁′ and h₁₁)+(phase difference between h₂₁ and h₂₁′).

$\begin{matrix} {{e^{{{j2\pi}({f_{1} - f_{1}^{\prime}})}\frac{\Delta d_{21}}{c}} = e^{j({\theta_{21} - \theta_{11} - \theta_{21}^{\prime} + \theta_{11}^{\prime}})}}{{\Delta d_{21}} = {{\frac{c}{2{\pi\left( {f_{1} - f_{1}^{\prime}} \right)}}\theta} = {\frac{c}{2\pi B}\theta}}}\left( {\theta = {\theta_{21} - \theta_{21}^{\prime} + \theta_{11}^{\prime} - \theta_{11}}} \right)} & (12) \end{matrix}$

A path difference Δd₃₁ between the GW station 70(1) and each of the FL antennas 211(1) and 211(3), and other path differences Δd₁₂, Δd₁₃, Δd₂₃, and Δd₃₂ can be obtained in the same manner.

Using the path differences Δd₂₁, Δd₃₁, Δd₁₂, Δd₁₃, Δd₂₃, and Δd₃₂, a propagation path response H_(fc) at a center frequency fsc of the transmission signal band of the feeder link can be estimated as in a H_(P) of the following equation (13), for example.

$\begin{matrix} {H_{P} = \begin{bmatrix} {❘h_{11}❘} & {{❘h_{12}❘}e^{j2\pi f_{sc}\frac{\Delta d_{12}}{c}}} & {{❘h_{13}❘}e^{j2\pi f_{sc}\frac{\Delta d_{13}}{c}}} \\ {{❘h_{21}❘}e^{j2\pi f_{sc}\frac{\Delta d_{21}}{c}}} & {❘h_{22}❘} & {{❘h_{23}❘}e^{j2\pi f_{sc}\frac{\Delta d_{23}}{c}}} \\ {{❘h_{31}❘}e^{j2\pi f_{sc}\frac{\Delta d_{31}}{c}}} & {{❘h_{32}❘}e^{j2\pi f_{sc}\frac{\Delta d_{32}}{c}}} & {❘h_{33}❘} \end{bmatrix}} & (13) \end{matrix}$

When each of the GW stations 70(1) to 70(3) transmits plural pilot signals as shown in FIG. 13 and FIG. 14 , it is possible to detect a path difference that is greater than or equal to wavelengths λ₁, λ₂, and λ₃ of each pilot signal. For example, assuming the LTE, a bandwidth B of a transmission signal band FB of the feeder link is 18 MHz, so that the Δd₂₁ can be estimated in a range within wavelength of a pilot frequency difference B as shown in the above equation (12). In the present example, it is possible to accurately estimate the range of 0<Δd₂₁<16 [m], which is a required range for implementation.

In the examples of FIG. 13 and FIG. 14 , since the plural pilot signals S_(P1), S_(P2), S_(P3) and the pilot signals S_(P1)′, S_(P2)′, S_(P3)′, which are respectively transmitted from the GW stations 70(1) to 70(3) and have frequencies f₁, f₂, f₃, f₂′, and f₃′ different from each other, are evenly distributed and arranged in the first guard band GB 1 and the second guard band GB2, each pilot signal can be separated by a filter and easily individually detected.

It is noted that, using the matrix H_(fc) (H_(P) of the above equation (13)) of the propagation path response, the weight used for the interference canceller can be calculated by, for example, the ZF (Zero-Forcing) method or the MMSE (Minimum Mean Square Error) method using the matrix of the propagation path response.

For example, in the ZF method, the weight W can be obtained by an inverse matrix of the matrix H_(fc) of the propagation path response as in the following equation (14). W=H _(fc) ⁻¹  (14)

In the MMSE method, the weight W can be used by the following equation (15). Herein, N_(T) is the number of transmitting antennas and γ is SNR.

$\begin{matrix} {W = {\left( {{H_{fc}^{H}H_{fc}} + \frac{N_{T}I_{N_{r}}}{\gamma}} \right)^{- 1}H_{fc}^{H}}} & (15) \end{matrix}$

In the above reference example, in the relay communication station 21 of the HAPS 20, in order to receive the pilot signals of different narrowband frequencies transmitted from each of the GW stations 70(1) to 70(3), plural pilot signal receivers and the narrowband reception filter 218 for separating the pilot signals are required. For example, in the example of FIG. 14 , three narrowband reception filters 218 are required for each of the guard bands. Further, it is necessary to increase the number of the pilot signal receivers depending on increase of the number of GW stations spatially multiplexed. In particular, since a frequency stability of an oscillation frequency is easy to deteriorate when the frequency of the pilot signal is high (for example, millimeter wave), an oscillation frequency circuit with high stability is indispensable for transmitting the pilot signals of the narrowband frequency. Since the number of narrowband reception filters of the relay communication station 21 increases and the oscillation frequency circuit with high stability becomes indispensable when the pilot signal of the narrowband frequency is used in this way, it is difficult to realize the relay communication station 21 having a simple configuration.

Therefore, in the present embodiment, by spectrally spreading the plural pilot signals transmitted and received between the GW stations 70(1) to 70(3) and the relay communication station 21 of the HAPS 20, a simple configuration that does not require the narrowband reception filter is realized in the relay communication station 21 that receives the pilot signal.

FIG. 17 is an illustration showing an example of spread-spectrum pilot signals in a transmission signal band of an uplink transmitted from the GW stations 70(1) to 70(3) according to an embodiment. FIG. 18 is an illustration showing an example of spread-spectrum pilot signals in a reception signal band of an uplink received by the HAPS 20 according to an embodiment. FIG. 19 is an illustration showing an example of pilot signals before inverse-spreading that is received by the HAPS 20 and separated by a filter according to an embodiment. FIG. 20 is an illustration showing an example of pilot signal groups after inverse-spreading according to an embodiment.

Each of the GW stations 70(1) to 70(3) spectrally spreads a plurality of pilot signals S_(P1), S_(P2), S_(P3), S_(P1)′, S_(P2)′, S_(P3)′ to be transmitted by using a plurality of transmission-side spreading codes orthogonal to each other (the code sequences are different from each other) as showing in FIG. 17 , and transmits the plurality of spread pilot signals at the same frequency in each guard band. The relay communication station 21 of the HAPS 20 extracts the spread pilot groups by using a filter 216 in each guard band, spectrally inverse-spreads from the extracted pilot signal groups using a plurality of reception-side spreading codes (inverse-spreading codes) corresponding to the plurality of transmission-side spreading codes, and separates each pilot signal (see FIG. 19 ) as shown in FIG. 18 . The relay communication station 21 of the HAPS 20 calculates the above-mentioned propagation path response h_(ki) based on the inverse-spread and separated pilot signals from each of the GW stations 70(1) to 70(3).

The calculation of the propagation path response h_(ki) using the spread-spectrum pilot signals can be performed, for example, as follows.

If a spreading length of the spectral spreading is set to N and a plurality of spreading codes orthogonal to each other are set to C_(i)(n), the relationship of the following equation (16) is established from the definition of orthogonality between the spreading codes. Herein, i and j are numbers for identifying the GW station 70 (GW antenna 71) (in the present example, i, j=1, 2, 3), and n is an identification number (n=1, 2, - - - , N) of plural codes in the spreading code (code series).

$\begin{matrix} {{\frac{1}{N}{\sum\limits_{n = 1}^{N}{{C_{i}(n)}{C_{j}(n)}}}} = \left\{ \begin{matrix} 1 & \left( {i = j} \right) \\ 0 & \left( {i \neq j} \right) \end{matrix} \right.} & (16) \end{matrix}$

If a transmission-target pilot signal transmitted from an i-th GW station 70(i) is set to S_(pi) and the spreading code is set to C_(i)(n), the transmission signal of the spread-spectrum pilot signal after spreading is C_(i)(n)S_(pi) (n<N). Herein, if a propagation path response of a k-th FL antenna 211(k) of the relay communication station 21 of the HAPS 20 from the GW station 70(i) is set to h_(ki), a reception signal X_(k)(n) of the pilot signal before inverse-spreading, which is received by a k-th FL antenna 211(k), can be represented by the following equation (17).

$\begin{matrix} {{X_{k}(n)} = {\sum\limits_{i = 1}^{N_{G}}{h_{ki}\left( {{C_{i}(n)}S_{pi}} \right)}}} & (17) \end{matrix}$

If a reception signal after inverse conversion of the pilot signal from the GW station 70(i) of the k-th FL antenna 211(k) of the relay communication station 21 of the HAPS 20 is set to P_(ki), the P_(ki) is obtained by the following equation (18) by inverse-spreading (multiplying) the reception signal X_(i)(n) of the received pilot signal with the spreading code C_(j)(n) of the j-th GW station 70(j).

$\begin{matrix} {P_{ki} = {{\frac{1}{N}{\sum\limits_{n = 1}^{N}{{X_{k}(n)}{C_{i}(n)}}}} = {{\frac{1}{N}{\sum\limits_{n = 1}^{N}{\left( {\sum\limits_{j = 1}^{N_{G}}{h_{kj}{C_{j}(n)}S_{pj}}} \right){C_{i}(n)}}}} = {{\underset{j = 1}{\sum\limits^{N_{G}}}{h_{kj}{S_{pj}\left( {\frac{1}{N}{\sum\limits_{n = 1}^{N}{{C_{j}(n)}{C_{i}(n)}}}} \right)}}} = {h_{ki}S_{pi}}}}}} & (18) \end{matrix}$

Since the pilot signal S_(pi) to be transmitted is known, the propagation path response h_(ki) is obtained by the above-described equation (5).

FIG. 21A is a functional block diagram showing an example of a transmitter 711(i) of the GW station 70(i). FIG. 21B is a spectrum diagram showing an example of a desired signal (S_(i)) and a spread pilot signal (C_(i)S_(pi)) that is spectrally spread in a transmission signal X_(i) transmitted from the transmitter 711(i) of the GW station 70(i). It is noted that, in FIG. 21A and FIG. 21B, although the pilot signal S_(pi) transmitted and received in the first guard band GB1 on the low frequency side described above is illustrated, the pilot signal S_(pi)′ of the second guard band GB2 on the high frequency side is spectrally spread and transmitted and received in the same manner.

In FIG. 21A and FIG. 21B, the pilot signal S_(pi) to be transmitted from the i-th GW station 70(i) is spectrally spread by multiplying the spreading code C_(i)(n) of the transmission-side in the i-th transmitter 711(i). The pilot signal C_(i)S_(pi) after spreading is added to the desired signal S_(i), which is a relay signal, to generate the transmission signal X_(i). The transmission signal X_(i) including the spread pilot signal C_(i)S_(pi) is amplified to a predetermined power by a high frequency amplifier 712(i) and transmitted from the GW antenna 71(i) to the HAPS 20.

FIG. 22A is a functional block diagram showing an example of a receiver 210(k) of the relay communication station 21 of the HAPS 20. FIG. 22B is a spectrum diagram showing an example of a desired signal (S_(i)) and a spread pilot signal (C_(i)S_(pi)) that is spectrally spread in a reception signal X_(i) received by a receiver 210(k) of the relay communication station 21 of the HAPS 20. It is noted that, in FIG. 22A and FIG. 22B, although the pilot signal S_(pi) transmitted and received in the first guard band GB1 on the low frequency side described above is illustrated, the pilot signal S_(pi)′ of the second guard band GB2 on the high frequency side is spectrally spread and transmitted and received in the same manner.

In FIG. 22A and FIG. 22B, the reception signal X_(i) from the i-th GW station 70(i) received by the k-th FL antenna 211(k) of the relay communication station 21 of the HAPS 20 is amplified by the high frequency amplifier 219(k) of the receiver 210(k), and then separated into the pilot signal C_(i)S_(pi) after spreading (before inverse-spreading) and the desired signal S_(i) which is a relay signal, by filters 216(k) and 217(k). The desired signal S_(i) is output to an interference suppression section (interference canceller).

On the other hand, the reception signal of the pilot signal after spreading (before inverse-spreading) included in the reception signal X_(i) is spectrally inverse-spread by multiplying by the spreading code C_(i)(n) on the reception-side corresponding to the spreading code C_(i)(n) on the transmission-side used in the i-th transmitter 711(i). The reception signal of the pilot signal after inverse-spreading is converted into the pilot signal h_(ki) after propagating in the propagation path of the feeder link by multiplying by an inverse number (1/S_(pi)) of the pilot signal S_(pi) to be transmitted, which is a known signal, and output as an element of the propagation path response H used in the interference suppression section (interference canceller).

FIG. 23 is an illustration showing an example of a main configuration of the relay communication station 21 of the HAPS 20 according to the present embodiment. In FIG. 23 , the relay communication station 21 is provided with a feeder-link communication section 221, a service-link communication section 222, a frequency conversion section 223, a control section 224 for controlling each section, and an interference suppression section 225.

The feeder-link communication section 221 is provided with plural receivers (see FIG. 22A) corresponding to the number of GW stations 70 (the number of FL antennas 211), and transmits and receives radio signals of a first frequency F1 for feeder link to and from the GW station 70 via the FL antenna 211.

The plural receivers 210 of the feeder-link communication section 221 receive a plurality of pilot signals after spreading on the same frequency, which are respectively transmitted from the plural GW stations 70(1) to 70(3), and separate the pilot signal groups, in which the plurality of spread pilot signals overlap, by a filter. Each receiver 210 spectrally inverse-spreads the reception signals of the plural spread pilot signals, which are separated by the filter, with a reception-side spreading code corresponding to a transmission-side spreading code, and outputs the inverse-spread pilot signal to the interference suppression section 225 as a reception result of the pilot signal h_(ki) propagating in the propagation path of the feeder link.

The service-link communication section 222 transmits and receives radio signals of a second frequency F2 for the service link to and from the terminal apparatus 61 via an antenna for service link 115. The frequency conversion section 223 performs frequency conversion between the first frequency F1 and the second frequency F2, between the feeder-link communication section 221 and the service-link communication section 222. The radio signals relayed by the relay communication station 21 may be transmitted and received, for example, by using the OFMDA communication method conforming to the LTE or LTE-Advanced standard. In this case, good communication quality can be maintained even if multipaths with different radio signal delays occur.

The control section 224 can control each section by executing a pre-installed program.

The interference suppression section 225 performs above-described estimation of the propagation path response, the calculation of the weight and the interference-cancellation signal process based on reception results (h_(ki)) of the plurality of inverse-spread pilot signals that are output from the feeder-link communication section 221, by executing a pre-installed program.

It is noted that, when receiving control information from a remote control apparatus (control source) of the communication operator of the mobile communication network or transmitting information to the remote control apparatus, a user terminal (mobile station) 226 connected to the control section 224 may be provided. The control section 224, for example, may receive control information transmitted from the remote control apparatus by the user terminal (mobile station) 226 and control each section based on the control information. Herein, the communication between the remote control apparatus and the user terminal (mobile station) 226 may be performed using, for example, the IP address (or telephone number) assigned to each of the remote control apparatus and the user terminal (mobile station) 226.

In the interference canceller in the above forward link, although the plural pilot signals S_(pi) and S_(pi)′ after spectrally spreading are distributed to each of the first guard band GB1 and the second guard band GB2 outside the transmission signal band FB and transmitted and received, at least one of the plural pilot signals S_(pi) and S_(pi)′ after spectral spreading may be transmitted and received within the transmission signal band FB. For example, as shown in FIG. 24 , of the plural pilot signals S_(pi) and S_(pi)′ after spectral spreading, the pilot signals S_(pi) on the lower frequency side may be transmitted and received within the transmission signal band FB, and the other pilot signals S_(pi)′ on the high frequency side may be transmitted and received in the second guard band GB2 outside the transmission signal band FB. Even when the pilot signals is transmitted and received within the transmission signal band FB in this way, since the pilot signals transmitted and received within the transmission signal band FB are spectrally spread, it is possible to reduce the interference of the pilot signals with respect to the desired signal Si in the transmission signal band FB, and it is possible to solve the interference within the transmission signal band due to the narrowband signal (pilot signal) by separation and error correction on the reception-side.

Next, a configuration and a method for reducing a reverse link interference between GW stations (between feeder links) in plural GW systems of the present embodiment are described.

[MIMO Interference Canceller (Reception Interference Canceller) of Reverse Link on GW Station Side (Reception-Side)]

FIG. 25A is an illustration showing an example of a schematic configuration of an interference canceller section 720 of a reverse link, which is provided on the GW station side (reception-side) in a multi-feeder link of plural GW systems according to an embodiment, and FIG. 25B is an illustration showing a relationship between a transmission signal S and a reception signal Y. The interference canceller section 720 is provided in, for example, a common apparatus 700 connected to transceivers of GW antennas 71(1), 71(2), 71(3) of the plural GW stations 70(1), 70(2), 70(3) by a communication line (interface).

It is noted that, the common apparatus 700 may be an apparatus (for example, remote control apparatuses, servers, etc. installed in communication centers, control centers, etc. of mobile communication networks) installed at a place where information is concentrated from the plural GW stations 70(1), 70(2), 70(3). Further, the interference canceller section 720 may be provided in any one of the GW stations 70(1), 70(2), 70(3) connected to each other by the communication line (interface), and data such as a reception result for interference cancellation, a propagation path response and a weight may be shared between the GW stations.

In FIG. 25A, for example, the GW antenna 71(1) receives a desired signal S1 (Y11) transmitted from the FL antenna 211(1) of the HAPS 20, an interference signal I2 (Y12) transmitted from the FL antenna 211(2) of the HAPS 20, and an interference signal I3 (Y13) transmitted from FL antenna 211(3) of the HAPS20. The reception signal AN1 is represented by the equation (1) described above.

In the interference canceller section 720, as shown in the equation (2) described above, by multiplying the signals S2 and S3 received by the other GW antennas 71(2) and 71(3) by the weights W2 and W3 respectively corresponding to the signals S2 and S3, and adding or subtracting them, the desired signal S1 (Y11) in which the interference signals I2 and I3 are canceled can be output. Similarly, for the desired signals S2 (Y22) and S3 (Y33) transmitted from the FL antennas 211(2) and 211(3) of the HAPS 20, the interference signals from the other FL antennas can be canceled.

The interference canceller section 720 can use a weight W calculated with a propagation path response matrix (propagation path response matrix H) by the ZF (Zero-Forcing) method. For example, the signal transmitted from the FL antenna 211(1) of the HAPS 20 is not only received as the desired signal S1 (Y11) by the GW antenna 71(1), but also received as interference signals I1 (Y12) and I1′ (Y13) by the GW antennas 71(2) and 71(3). Further, the signal transmitted from the FL antenna 211(2) of the HAPS 20 is not only received as an interference signal I2 (Y21) by the GW antenna 71(1), but also received as an interference signal I2′ (Y23) by the GW antenna 71(3). Moreover, the signal transmitted from the FL antenna 211(3) of the HAPS 20 is not only received as an interference signal I3 (Y31) by the GW antenna 71(1), but also received as an interference signal I3′ (Y32) by the GW antenna 71(2). In the interference canceller section 720, these interference signals I1, I1′, I2′ and I3′ are considered, and the desired signal S1 (Y11) is outputted, for example, as shown in the above-described equation (3). As a result, the accuracy of interference suppression in the reverse link between GW stations (between feeder links) can be improved.

In order to calculate the weight W used for the interference canceller section (MIMO interference canceller) 720, it is necessary to grasp propagation path responses (propagation path response matrix H) between the GW antennas 71(1) to 71(3) of the GW stations 70(1) to 70(3) and the FL antennas 211(1) to 211(3) of the HAPS 20. In particular, in the plural GW systems of the present embodiment, since an airship of the HAPS 20 moves relative to the GW antennas 71(1) to 71(3) of the GW stations 70(1) to 70(3), the propagation path responses (propagation path response matrix H) also change according to the movement.

Therefore, in the present embodiment, in order to grasp the propagation path response (propagation path response matrix H), the pilot signals are spectrally spread by a plurality of transmission-side spreading codes orthogonal to each other, and the plurality of spread pilot signals are transmitted on the same frequency, from each of the FL antennas 211(1) to 211(3) of the HAPS 20. The interference canceller section 720 spectrally inverse-spreads the spread pilot signals received from each of the FL antennas 211(1) to 211(3), with a plurality of reception-side spreading codes corresponding to the plurality of transmission-side spreading codes, estimates propagation path response (propagation path response matrix H) of the center frequency fsc of the transmission signal band of the feeder link based on reception results of the inverse-spread pilot signals, and derives a weight W.

The plural spread pilot signals transmitted from each of the FL antennas 211(1) to 211(3) of the HAPS 20 may be arranged, for example, in a first guard band GB1 that is a first adjacent band of a transmission signal band FB of the feeder link for transmitting the desired signals S1, S2, S3, which is adjacent to the transmission signal band FB from low frequency side, or may be arranged in a second guard band GB2 that is a second adjacent band adjacent to the transmission signal band FB from high frequency side. The plural pilot signals after spreading may be arranged in both of the first guard band GB1 and the second guard band GB2. The pilot signals transmitted from each of the FL antennas 211(1) to 211(3) may be a single pilot signal or plural pilot signals.

In the interference canceller section 720 provided on the GW station side (reception-side) of FIG. 25A, since the GW antennas 71(1) to 71(3) of the GW station 70(1) to 70(3) are far from each other (for example, by a separation distance of 50 to 100 km), for example, the common apparatus 700 or any one of the GW stations 70(1) to 70(3) performs the following processing.

(1) The propagation path response matrix H is generated by collecting the propagation path response that is respectively received and measured plural spread pilot signals by the GW antennas 71(1) to 71(3), or exchanging the propagation path responses with each other between the GW stations.

(2) The weight W of the interference canceller is determined, and the interference of the inverse-link reception signal received by each receiver is canceled.

Since the GW antennas 71(1) to 71(3) are far away from each other, a delay occurs between the receivers of GW stations 70(1) to 70(3). Therefore, a highly accurate time synchronization between the GW stations 70(1) to 70(3) is required in consideration of the separation distance between the common apparatus 700 and the receivers of GW stations 70(1) to 70(3) or the separation distance between the receivers of GW stations 70(1) to 70(3). Further, a transmission line for collecting the propagation path responses of the GW stations 70(1) to 70(3) or exchanging the propagation path responses with each other between the GW stations is also required, which complicates the processing of the interference canceller section 720.

Therefore, as shown below, an interference canceller of the reverse link in the multi-feeder link may be provided on the HAPS 20 side.

[MIMO Interference Canceller of Reverse Link Equipped with HAPS (Transmission Interference Canceller)]

FIG. 26A is an illustration showing an example of a schematic configuration of an interference canceller section 220 of the reverse link provided on the HAPS 20 side (transmission-side) in the multi-feeder link of the plural GW systems according to yet another embodiment, and FIG. 26B is an illustration showing a relationship between the transmission signal S and the reception signal Y. The interference canceller section 220 in FIG. 26A has a function of a transmission interference canceller that suppresses an interference from another transmitter in the HAPS 20 with respect to reception signals of respective GW stations 70(1) to 70(3), by multiplying a transmission signal of each transmitter in the HAPS 20 having a short distance between transmitters (for example, several meters) by a weight (hereinafter referred to as “transmission weight”) W and transmitting it.

In the example of the interference canceller section 220 in FIG. 26A, the interference canceling process is performed by the transmitter of the HAPS 20, and the interference canceling process is not performed by the receiver on the GW station side where the distance between the receivers is long (50 to 100 km). In order to calculate the transmission weight W by the interference canceller section 220, the propagation path response matrix H in the propagation path of the downlink, which is the reverse link of the feeder link, from the HAPS 20 to each of the GW stations 70(1) to 70(3) is required.

Since the airship of the HAPS 20 moves relative to the GW antennas 71(1) to 71(3) of the GW stations 70(1) to 70(3) as described above, the downlink propagation path response (propagation path response matrix H) also changes according to the movement. Therefore, also in the present example, in order to grasp the propagation path response (propagation path response matrix H), plural pilot signals, which are transmitted and received by spectrally spreading with plural spreading codes orthogonal to each other, are used. The interference canceller section 220 estimates the propagation path response (propagation path response matrix H) of the center frequency fsc of the transmission signal band of the feeder link based on the pilot signal, and derives the transmission weight W.

The pilot signal is arranged, for example, in the first guard band GB1, the second guard band GB2 or both of them, wherein the guard band is adjacent to the transmission signal band FB of the feeder link in which the desired signals S1, S2, and S3 are transmitted shown in FIG. 17 and FIG. 18 described above.

As a method of estimating the propagation path response (propagation path response matrix H) of the feeder link and calculating the transmission weight W, for example, there are a method of using a downlink pilot signal and a method of using an uplink pilot signal.

[Calculation Method of Transmission Weight W Using Downlink Pilot Signal]

First, it is described of a case of using a downlink pilot signal.

In the present calculation method, pilot signals Ci(n) S_(Pi) (i=1 to 3) of the same frequency, which are arranged in the guard bands outside the transmission signal band FB and spectrally spread by a spreading code Ci(n) orthogonal to each other, are transmitted from each transmitter of the HAPS 20 to the GW stations 70(1) to 70(3) via each of the FL antennas 211(1) to 211(3).

Next, each of the GW stations 70 (1) to 70 (3) inverse-spreads a reception signal received from the HAPS 20 and separates each of the pilot signals S_(Pi) (i=1 to 3) (see FIG. 15 described above), and obtains a propagation path response hki from the FL antenna 211(i) of the i-th transmitter of the HAPS 20 to the k-th GW station 70(k), from the separated pilot signal S_(Pi). Each of the GW stations 70(1) to 70(3) transfers information on the obtained propagation path response h_(ki) (see equations (4) and (5) described above) to the interference canceller section 220 via the transmitter/receiver of the HAPS 20 as feedback information using an uplink control signal.

Next, the interference canceller section 220 of the HAPS 20 obtains a downlink-propagation path response matrix H_(P) (see the following equation (19)) of the pilot signal S_(pi), based on a downlink-propagation path response h_(ki) (see equation (6) described above) of each of the GW stations 70(1) to 70(3), which is transferred by the uplink control signal.

$\begin{matrix} {{H_{P} = {\begin{bmatrix} {h_{11}\left( f_{P1} \right)} & {h_{12}\left( f_{P2} \right)} & {h_{13}\left( f_{P3} \right)} \\ {h_{21}\left( f_{P1} \right)} & {h_{22}\left( f_{P2} \right)} & {h_{23}\left( f_{P3} \right)} \\ {h_{31}\left( f_{P1} \right)} & {h_{32}\left( f_{P2} \right)} & {h_{33}\left( f_{P3} \right)} \end{bmatrix} = \text{ }{\begin{bmatrix} {{❘{h_{11}\left( f_{P1} \right)}❘}e^{j\theta_{11}}} & {{❘{h_{12}\left( f_{P2} \right)}❘}e^{j\theta_{12}}} & {{❘{h_{13}\left( f_{P3} \right)}❘}e^{j\theta_{13}}} \\ {{❘{h_{21}\left( f_{P1} \right)}❘}e^{j\theta_{21}}} & {{❘{h_{22}\left( f_{P2} \right)}❘}e^{j\theta_{22}}} & {{❘{h_{23}\left( f_{P3} \right)}❘}e^{j\theta_{23}}} \\ {{❘{h_{31}\left( f_{P1} \right)}❘}e^{j\theta_{31}}} & {{❘{h_{32}\left( f_{P2} \right)}❘}e^{j\theta_{32}}} & {{❘{h_{33}\left( f_{P3} \right)}❘}e^{j^{\theta_{33}}}} \end{bmatrix} = \text{ }\begin{bmatrix} {❘{h_{11}\left( f_{P1} \right)}❘} & {{❘{h_{12}\left( f_{P2} \right)}❘}e^{j2\pi f_{P2}\frac{\Delta d_{12}}{c}}} & {{❘{h_{13}\left( f_{P3} \right)}❘}e^{j2\pi f_{P3}\frac{\Delta d_{13}}{c}}} \\ {{❘{h_{21}\left( f_{P1} \right)}❘}e^{j2\pi f_{P1}\frac{\Delta d_{21}}{c}}} & {❘{h_{22}\left( f_{P2} \right)}❘} & {{❘{h_{23}\left( f_{P3} \right)}❘}e^{j2\pi f_{P3}\frac{\Delta d_{23}}{c}}} \\ {{❘{h_{31}\left( f_{P1} \right)}❘}e^{j2\pi f_{P1}\frac{\Delta d_{31}}{c}}} & {{❘{h_{32}\left( f_{P2} \right)}❘}e^{j2\pi f_{P2}\frac{\Delta d_{32}}{c}}} & {❘{h_{33}\left( f_{P3} \right)}❘} \end{bmatrix}}}}\text{ }\begin{bmatrix} e^{j2\pi f_{P1}\frac{d_{11}}{c}} & 0 & 0 \\ 0 & e^{j2\pi f_{P2}\frac{d_{22}}{c}} & 0 \\ 0 & 0 & e^{j2\pi f_{P3}\frac{d_{33}}{c}} \end{bmatrix}} & (19) \end{matrix}$

The interference canceller section 220 of the HAPS 20 estimates a propagation path response matrix H (f_(d)) of an arbitrary frequency f_(d) in the transmission signal band FB (see the following equation (20)), based on the propagation path response matrix H_(P) of the pilot signal S_(P1) (see equation (7) above).

$\begin{matrix} {{H\left( f_{d} \right)} \approx \text{ }\begin{bmatrix} {❘{h_{11}\left( f_{d} \right)}❘} & {{❘{h_{12}\left( f_{d} \right)}❘}e^{j2\pi f_{d}\frac{\Delta d_{12}}{c}}} & {{❘{h_{13}\left( f_{d} \right)}❘}e^{j2\pi f_{d}\frac{\Delta d_{13}}{c}}} \\ {{❘{h_{21}\left( f_{d} \right)}❘}e^{j2\pi f_{d}\frac{\Delta d_{21}}{c}}} & {❘{h_{22}\left( f_{d} \right)}❘} & {{❘{h_{23}\left( f_{d} \right)}❘}e^{j2\pi f_{d}\frac{\Delta d_{23}}{c}}} \\ {{❘{h_{31}\left( f_{d} \right)}❘}e^{j2\pi f_{d}\frac{\Delta d_{31}}{c}}} & {{❘{h_{32}\left( f_{d} \right)}❘}e^{j2\pi f_{d}\frac{\Delta d_{32}}{c}}} & {❘{h_{33}\left( f_{d} \right)}❘} \end{bmatrix}} & (20) \end{matrix}$

Herein, Δd_(ki) (k=1 to 3, i=1 to 3) in the above equation (20) is a difference in path length (path difference) between the i-th FL antenna 211(i) on the transmission-side and the GW antenna 71(k) of the k-th GW station 70(k) on the reception-side in the downlink. If the number k (=i) of the GW antenna 71 of the GW station 70, which is the most face-to-face with the i-th FL antenna 211(i), is expressed as i for convenience, when the path length of the interference signal between the k-th GW antenna 71(k) and the i (≠k)-th FL antenna 211(i) is d_(ki) with reference to the path length d_(ii) of the desired signal between the i-th GW antenna 71(i) and the i-th FL antenna 211(i) that is the most face-to-face with the i-th GW antenna 71(i), the Δd_(ki) is a difference (path difference) between the path length d_(ii) of the desired signal and the path length d_(ki) of the interference signal with reference to the path length d_(ii) of the desired signal. For example, with reference to the path length d_(ii) between the first GW antenna 71(1) and the first FL antenna 211(1) that is the most face-to-face with the first GW antenna 71(1), Δd₁₂ is a difference (path difference) between the reference path length d₁₁ and the path length d₁₂ between the first GW antenna 71(1) and the second FL antenna 211(2). Further, with reference to the path length d₂₂ between the second GW antenna 71(2) and the second FL antenna 211(2) that is the most face-to-face with the second GW antenna 71(2), Δd₂₁ is a difference (path difference) between the reference path length d₂₂ and the path length d₂₁ between the second GW antenna 71(2) and the first FL antenna 211(1).

The foregoing Δd_(ki) can be expressed by the phase difference Δθ_(ki) between the propagation path response h_(ki) of the interference signal and the propagation path response h_(ii) of the desired signal as in the following equation (21).

$\begin{matrix} {{\Delta d_{ki}} = {\frac{c}{2{\pi\left( {f_{Pi}^{\prime} - f_{Pi}} \right)}}\left( {{\Delta\theta}_{ki}^{\prime} - {\Delta\theta}_{ki}} \right)}} & (21) \end{matrix}$

In the above equation (21), Δθ_(ki) is a phase difference between h_(ki) and h_(ii) of the propagation path response, and Δθ′_(ki) is a phase difference between h′_(ki) and h′_(ii) of the propagation path response (see the following equations (22) and (23)).

$\begin{matrix} \begin{matrix} {{\Delta\theta_{ki}} = {\theta_{ki} - \theta_{ii}}} \\ {= {{Arg}\left( \frac{h_{ki}}{h_{ii}} \right)}} \end{matrix} & (22) \end{matrix}$ $\begin{matrix} \begin{matrix} {{\Delta\theta}_{ki}^{\prime} = {\theta_{ki}^{\prime} - \theta_{ii}^{\prime}}} \\ {= {{Arg}\left( \frac{h_{ki}^{\prime}}{h_{ii}^{\prime}} \right)}} \end{matrix} & (23) \end{matrix}$

Further, as exemplified in the following equation (24), it is assumed that the propagation path response h_(ki)(f_(Pi)) at the frequency f_(Pi) of the pilot signal S_(Pi) arranged in the guard band and the propagation path response h_(ki)(f_(d)) at the frequency f_(d) in the transmission signal band FB are equivalent to each other. |h ₁₁(f _(p1))|≈|h ₁₁(f _(d))|,|h ₁₂(f _(p1))|≈|h ₁₂(f _(d))|,|h ₁₃(f _(p1))|≈|h ₁₃(f _(d))| |h ₂₁(f _(p1))|≈|h ₂₁(f _(d))|,|h ₂₂(f _(p1))|≈|h ₂₂(f _(d))|,|h ₂₃(f _(p1))|≈|h ₂₃(f _(d))| |h ₃₁(f _(p1))|≈|h ₃₁(f _(d))|,|h ₃₂(f _(p1))|≈|h ₃₂(f _(d))|,|h ₃₃(f _(p1))|≈|h ₃₃(f _(d))|

The interference canceller section 220 of the HAPS 20 calculates a transmission weight W(f_(d)) to be applied to a transmission signal having the frequency f_(d) in the transmission signal band FB transmitted from each of the FL antennas 211(1) to 211(3), based on the estimation result of the propagation path response H(f_(d)) of the frequency f_(d) in the transmission signal band FB represented by the above equation (20). For example, in the ZF (Zero-Forcing) method, a weight W_(ZF)(f_(d)) can be obtained by the inverse matrix of the propagation path response matrix H(f_(d)) as in the following equation (25). W _(ZF)(f _(d))=H ⁻¹(f _(d))=[w ₁(f _(d)),w ₂(f _(d)),w ₃(f _(d))]  (25)

When applying to actual communication, with respect to the weight W_(ZF)(f_(d)) obtained by the above ZF method, a transmission weight W(f_(d)) of the following equation (26), which is normalized so as to have a relative power of 1 in order not to increase the transmission power, may be used.

$\begin{matrix} {{W\left( f_{d} \right)} = \left\lbrack {\frac{w_{1}\left( f_{d} \right)}{{w_{1}\left( f_{d} \right)}},\frac{w_{2}\left( f_{d} \right)}{{w_{2}\left( f_{d} \right)}},\frac{w_{3}\left( f_{d} \right)}{{w_{3}\left( f_{d} \right)}}}\  \right\rbrack} & (26) \end{matrix}$ ${{norm} = \left\lbrack {{w_{1}\left( f_{d} \right)},{w_{2}\left( f_{d} \right)},{w_{3}\left( f_{d} \right)}} \right\rbrack}\text{ }{\begin{bmatrix} {1/{{w_{1}\left( f_{d} \right)}}} & 0 & 0 \\ 0 & {1/{{w_{2}\left( f_{d} \right)}}} & 0 \\ 0 & 0 & {1/{{w_{3}\left( f_{d} \right)}}} \end{bmatrix}\left( {{}:{norm}} \right)}$

When the transmission signal having the frequency f_(d) in the transmission signal band FB is multiplied by the transmission weight W(f_(d)) and transmitted from each of the FL antennas 211(1) to 211(3), a reception signal at the GW stations 70(1) to 70(3) is, for example, the following equation (27). In the equation (27), S_(d) is a transmission signal (desired signal) transmitted from the HAPS 20 to the GW station 70 at a frequency f_(d) in the transmission signal band FB, and N is noise.

$\begin{matrix} {Y = {{{{H\left( f_{d} \right)}\left( {{W\left( f_{d} \right)}S_{d}} \right)} + N} = {{{{H\left( f_{d} \right)}\left( {{H\left( f_{d} \right)}^{- 1}S_{d}} \right)} + N} = {{{\begin{bmatrix} {1/{{w_{1}\left( f_{d} \right)}}} & 0 & 0 \\ 0 & {1/{{w_{2}\left( f_{d} \right)}}} & 0 \\ 0 & 0 & {1/{{w_{3}\left( f_{d} \right)}}} \end{bmatrix}S_{d}} + N} \approx {\begin{bmatrix} {S_{d1}/{{w_{1}\left( f_{d} \right)}}} \\ {S_{d2}/{{w_{2}\left( f_{d} \right)}}} \\ {S_{d3}/{{w_{3}\left( f_{d} \right)}}} \end{bmatrix}\left( {S_{d}\operatorname{>>}N} \right)}}}}} & (27) \end{matrix}$

As exemplified in the above equation (27), in the reception signal Y received by each of the GW stations 70(1) to 70(3) in the reverse link of the multi-feeder link with the HAPS 20, interference from transmitters (FL antennas) other than the corresponding transmitter (FL antenna) of the HAPS 20 can be canceled.

[Calculation Method of Transmission Weight W Using Uplink Pilot Signal]

Next, it is described of a case of using an uplink pilot signal.

In the present calculation method, each of the GW stations 70(1) to 70(3) transmits pilot signals S_(Pi) and S_(Pi)′ by spreading them with a plurality of transmission-side spreading codes orthogonal to each other. Since a communication line for transmitting the spread pilot signals S_(P1) and S_(P1)′ is the uplink (forward link) in the opposite direction to the downlink (reverse link) for transmitting the transmission signal from the HAPS 20, the pilot signals S_(Pi) and S_(Pi)′ may be arranged in the transmission signal band FB of the reverse link.

The HAPS 20 receives the spread pilot signals S_(Pi) and S_(Pi)′ of the uplink (forward link) transmitted from each of the GW stations 70(1) to 70(3), and spectrally inverse-spreads them with a reception-side spreading code corresponding to a transmission-side spreading code. The interference canceller section 220 obtains a propagation path response matrix of uplink pilot signals based on reception results of the uplink pilot signals S_(Pi) and S_(Pi)′ after inverse-spreading by a propagation path model considering a free space transmission. Further, the interference canceller section 220 estimates a propagation path response matrix of a transmission signal in a transmission signal band FB of a downlink (reverse link) by using the propagation path response matrix of the uplink pilot signals.

Since each of the propagation path response matrix H_(P) by the uplink pilot signal S_(Pi), the propagation path response matrix H(f_(d)) of the frequency f_(d) of the downlink transmission signal band estimated based on the uplink pilot signal, the weight W_(ZF)(f_(d)) obtained by the ZF method, the normalized transmission weight W(f_(d)) and the reception signal at the GW station 70 is the same as those of the above-mentioned equations (19), (20), (25), (26) and (27), their description is omitted.

In case of calculating the transmission weight W using the uplink pilot signal, in the reception signal Y received by each of the GW stations 70(1) to 70(3) in the reverse link of the multi-feeder link with the HAPS 20, an interference from transmitters (FL antennas) other than the corresponding transmitter (FL antenna) of the HAPS 20 can be canceled.

As described above, the configuration using the interference canceller section 220, which is provided in the HAPS 20 for transmitting signals of the reverse link that is the downlink of the feeder link, simplifies the system configuration, since the distance between the transmitters that transmit signals to which the transmission weight W is applied is short (several meters), the configuration is a transmission interference canceller that multiplies the transmission signal of each transmitter on the HAPS 20 by the transmission weight (W) to suppress an interference from other transmitters of the reception signal of each GW station 70, and the receiver on the GW station side, which is far from the receiver (50 to 100 km), does not perform an interference cancellation processing.

Especially, in the calculation method of the transmission weight W of the downlink (reverse link) using the pilot signal of the uplink (forward link), it is not necessary to insert the pilot signal outside the transmission band in order to estimate the propagation path response matrix on the downlink, and the system configuration is further simplified.

It is noted that, in case that the relay communication station 21 of the HAPS 20 suppresses the interference of the reverse link as the transmission-side of the desired signal according to the embodiment, a main configuration of the relay communication station 21 may be the same as that in FIG. 23 described above.

In this case, the feeder-link communication section 221 in FIG. 23 is provided with plural receivers and transmitters corresponding to the number of GW stations 70 (the number of FL antennas 211), and performs a reception process and a transmission process of pilot signals as exemplified in the following (1) to (6) by executing a program incorporated in advance.

(1) Process for receiving a plurality of spread pilot signals of the same frequency transmitted from plural GW stations 70(1) to 70(3).

(2) Process for separating pilot signal groups in which the plurality of spread pilot signals overlap, with a filter.

(3) Process for spectrally inverse-spreading the plurality of spread pilot signals.

(4) Process for outputting the inverse-spread pilot signal to the interference suppression section 225 as a reception result of the pilot signal h_(ki) propagating in the propagation path of the feeder link.

(5) Process for spectrally spreading the plurality of pilot signals to be transmitted on the downlink (reverse link) on the same frequency, with a plurality of transmission-side spreading codes orthogonal to each other (code series are different from each other). (6) Process for transmitting the pilot signal groups in which spread pilot signals are duplicated to plural GW stations 70(1) to 70(3).

The interference suppression section 225 in FIG. 23 corresponds to the interference canceller section 220 described above, and performs the aforementioned process for suppressing the interference of the reverse link between the plural feeder links that is formed between the plural GW stations 70(1) to 70(3) and the HAPS, as exemplified in the following (1) to (3) by executing a pre-installed program.

(1) Process for estimating the plural propagation path responses based on the reception results of the plurality of pilot signals after inverse-spreading.

(2) Process for calculating a weight W based on the plural estimated propagation path responses, or process for calculating a weight W based on the plural propagation path responses received from any one of the plural GW stations 70(1) to 70(3) or a common apparatus. (3) With respect to each of the plural GW stations 70(1) to 70(3), signal process for adding or subtracting, for a transmission signal to the GW station, a transmission signal corresponding to the other GW station by the weight W corresponding to the other GW station.

As described above, according to the present embodiment, it is possible to dynamically suppress the interference between the plural feeder links in the multi-feeder links of the same frequency between the HAPS 20 and the plural GW stations 70(1) to 70(3).

In particular, according to the present embodiment, since it is not necessary to use narrowband pilot signals as plural pilot signals transmitted and received between the HAPS 20 and the plural GW stations 70(1) to 70(3), there is no need to provide a highly stable oscillation frequency circuit for transmitting narrowband pilot signals on a transmission-side, and a narrowband reception filter for separating narrowband pilot signals on a reception-side becomes unnecessary. Therefore, a dynamic suppression of interference in a multi-feeder link of HAPS can be realized with a simple configuration.

Further, according to the present embodiment, the path difference between the HAPS 20 and the plural GW stations 70(1) to 70(3) required for the dynamic suppression of the interference in the multi-feeder link can be estimated and grasped, up to the range required for implementing, so that the interference in the multi-feeder link can be suppressed accurately.

Further, according to the present embodiment, it is possible to improve the frequency utilization efficiency of the feeder link while suppressing the decrease in the SINR of the reverse link of the feeder link of the HAPS 20.

It is noted that, the process steps and configuration elements of the relay communication station of the communication relay apparatus such as the HAPS, the feeder station, the gateway station, the management apparatus, the monitoring apparatus, the remote control apparatus, the server, the terminal apparatus (user apparatus, mobile station, communication terminal), the base station and the base station apparatus described in the present description can be implemented with various means. For example, these process steps and configuration elements may be implemented with hardware, firmware, software, or a combination thereof.

With respect to hardware implementation, means such as processing units or the like used for establishing the foregoing steps and configuration elements in entities (for example, radio relay station, feeder station, gateway station, base station, base station apparatus, radio-relay station apparatus, terminal apparatus (user apparatus, mobile station, communication terminal), management apparatus, monitoring apparatus, remote control apparatus, server, hard disk drive apparatus, or optical disk drive apparatus) may be implemented in one or more of an application-specific IC (ASIC), a digital signal processor (DSP), a digital signal processing apparatus (DSPD), a programmable logic device (PLD), a field programmable gate array (FPGA), a processor, a controller, a microcontroller, a microprocessor, an electronic device, other electronic unit, computer, or a combination thereof, which are designed so as to perform a function described in the present specification.

With respect to the firmware and/or software implementation, means such as processing units or the like used for establishing the foregoing configuration elements may be implemented with a program (for example, code such as procedure, function, module, instruction, etc.) for performing a function described in the present specification. In general, any computer/processor readable medium of materializing the code of firmware and/or software may be used for implementation of means such as processing units and so on for establishing the foregoing steps and configuration elements described in the present specification. For example, in a control apparatus, the firmware and/or software code may be stored in a memory and executed by a computer or processor. The memory may be implemented within the computer or processor, or outside the processor. Further, the firmware and/or software code may be stored in, for example, a medium capable being read by a computer or processor, such as a random-access memory (RAM), a read-only memory (ROM), a non-volatility random-access memory (NVRAM), a programmable read-only memory (PROM), an electrically erasable PROM (EEPROM), a FLASH memory, a floppy (registered trademark) disk, a compact disk (CD), a digital versatile disk (DVD), a magnetic or optical data storage unit, or the like. The code may be executed by one or more of computers and processors, and a certain aspect of functionalities described in the present specification may by executed by a computer or processor.

The medium may be a non-transitory recording medium. Further, the code of the program may be executable by being read by a computer, a processor, or another device or an apparatus machine, and the format is not limited to a specific format. For example, the code of the program may be any of a source code, an object code, and a binary code, and may be a mixture of two or more of those codes.

The description of embodiments disclosed in the present specification is provided so that the present disclosures can be produced or used by those skilled in the art. Various modifications of the present disclosures are readily apparent to those skilled in the art and general principles defined in the present specification can be applied to other variations without departing from the spirit and scope of the present disclosures. Therefore, the present disclosures should not be limited to examples and designs described in the present specification and should be recognized to be in the broadest scope corresponding to principles and novel features disclosed in the present specification.

REFERENCE SIGNS LIST

-   20 HAPS (communication relay apparatus) -   21 relay communication station -   61 terminal apparatus -   70, 70(1) to 70(3) gate way station (GW station) -   71, 71(1) to 71(3) antenna for feeder link (GW antenna) -   200C, 200C(1) to 200C(7) three dimensional cell -   200F, 200F(1) to 200F(7) foot print -   210 receiver -   211, 211(1) to 211(3) antenna for feeder link (FL antenna) -   212, 212(1) to 212(3) antenna directional beam -   215 antenna for service link (SL antenna) -   216 filter for pilot signal -   217 filter for desired signal -   218 narrowband reception filter -   219 high frequency amplifier -   220 interference canceller section -   221 feeder-link communication section -   222 service-link communication section -   223 frequency conversion section -   224 control section -   225 interference suppression section -   700 common apparatus -   711 transmitter -   712 high frequency amplifier -   720 interference canceller section 

The invention claimed is:
 1. A system comprising an aerial-staying type communication relay apparatus including a relay communication station that relays radio communication of a terminal apparatus, the system comprising: plural gateway stations that are time-synchronized with each other and transmit and receive relay signals different from each other on a same frequency in a feeder link to and from the relay communication station of the aerial-staying type communication relay apparatus; means for transmitting and receiving a plurality of pilot signals that are spread spectrally using a plurality of spreading codes orthogonal to each other between the relay communication station and the plural gateway stations; means for estimating plural propagation path responses between the plural gateway stations and an antenna for feeder link of the communication relay apparatus in a transmission signal band of the feeder link based on reception results of spectral inverse-spreading of the plurality of pilot signals; means for calculating plural weights respectively corresponding to the plural gateway stations based on the plural propagation path responses; and means for subtracting, from a signal to be transmitted and received via a directional beam corresponding to the gateway station, a signal to be transmitted and received via the directional beam corresponding to the other gateway station that is multiplied by the weight corresponding to the other gateway station, with respect to each of the plural gateway stations.
 2. The system according to claim 1, wherein the relay communication station comprises a feeder-link communication section that transmits and receives relay signals different from each other on the same frequency in the feeder link to and from the plural gateway stations, and an interference suppression section that suppresses an interference between plural feeder links formed with the plural gateway stations, wherein the plural gateway stations transmit a plurality of spread pilot signals that are spectrally spread with a plurality of transmission-side spreading codes orthogonal to each other, to the relay communication station, wherein the feeder-link communication section of the relay communication station: receives the plurality of spread pilot signals from the plural gateway stations; and spectrally inverse-spreads reception signals of the plurality of spread pilot signals with a reception-side spreading code corresponding to the transmission-side spreading code, and wherein the interference suppression section of the relay communication station: estimates the plural propagation path responses between the plural gateway stations and the antenna for the feeder link of the communication relay apparatus in a transmission signal band of the feeder link, based on reception results of the plurality of inverse-spread pilot signals that are spectrally inverse-spread; calculates plural weights respectively corresponding to the plural gateway stations based on the plural propagation path responses; and subtracts, from a reception signal received by the directional beam corresponding to the gateway station, a reception signal received by the directional beam corresponding to the other gateway station that is multiplied by the weight corresponding to the other gateway station, with respect to each of the plural gateway stations.
 3. The system according to claim 1, wherein the relay communication station comprises a feeder-link communication section that transmits and receives relay signals different from each other on the same frequency in the feeder link to and from the plural gateway stations, and an interference suppression section that suppresses an interference between plural feeder links formed with the plural gateway stations, wherein the feeder-link communication section of the relay communication station transmits a plurality of spread pilot signals that are spectrally spread with a plurality of transmission-side spreading codes orthogonal to each other, wherein the plural gateway stations: receives the plurality of spread pilot signals from the relay communication station; and spectrally inverse-spreads reception signals of the plurality of spread pilot signals with a reception-side spreading code corresponding to the transmission-side spreading code, wherein any one of the gateway stations of the plural gateway stations or a common apparatus common to each gateway station: estimates the plural propagation path responses between the gateway station and the antenna for the feeder link of the communication relay apparatus in a transmission signal band of the feeder link, based on reception results of the plurality of inverse-spread pilot signals that are spectrally inverse-spread; transmits estimation results of the propagation path responses to the relay communication station, wherein the feeder-link communication section of the relay communication station receives the plural propagation path responses transmitted from the any one of the gateway stations or the common apparatus, and wherein the interference suppression section of the relay communication station: calculates a weight for suppressing an interference signal that causes an interference by a transmission signal transmitted from the relay communication station to the gateway station and received by another gateway station, based on the plural propagation path responses, with respect to each of the plural gateway stations; and adds or subtracts, for the transmission signal to be transmitted to the gateway station, a transmission signal to be transmitted to another gateway station that is multiplied by the weight corresponding to the other gateway station, with respect to each of the plural gateway stations.
 4. The system according to claim 1, wherein the relay communication station comprises a feeder-link communication section that transmits and receives relay signals different from each other on the same frequency in the feeder link to and from the plural gateway stations, and an interference suppression section that suppresses an interference between plural feeder links formed with the plural gateway stations, wherein the feeder-link communication section of the relay communication station transmits a plurality of spread pilot signals that are spectrally spread with a plurality of transmission-side spreading codes orthogonal to each other, wherein the plural gateway stations: receives the plurality of spread pilot signals from the relay communication station; spectrally inverse-spreads reception signals of the plurality of spread pilot signals with a reception-side spreading code corresponding to the transmission-side spreading code; and transmits reception results of the plurality of inverse-spread pilot signals that are spectrally inverse-spread, to the relay communication station, wherein the feeder-link communication section of the relay communication station receives the reception results of the plurality of inverse-spread pilot signals transmitted from each of the plural gateway stations, wherein the interference suppression section of the relay communication station: estimates the plural propagation path responses between the gateway station and the antenna for the feeder link of the communication relay apparatus in a transmission signal band of the feeder link, based on the reception results of the plurality of pilot signals received from each of the plural gateway stations; calculates a weight for suppressing an interference signal that causes an interference by a transmission signal transmitted from the relay communication station to the gateway station and received by another gateway station, based on estimation results of the plural propagation path responses, with respect to each of the plural gateway stations; and adds or subtracts, for the transmission signal to be transmitted to the gateway station, a transmission signal to be transmitted to another gateway station that is multiplied by the weight corresponding to the other gateway station, with respect to each of the plural gateway stations.
 5. The system according to claim 1, wherein the relay communication station comprises a feeder-link communication section that transmits and receives relay signals different from each other on the same frequency in the feeder link to and from the plural gateway stations, and an interference suppression section that suppresses an interference between plural feeder links formed with the plural gateway stations, wherein the feeder-link communication section of the relay communication station transmits a plurality of spread pilot signals that are spectrally spread with a plurality of transmission-side spreading codes orthogonal to each other, wherein the plural gateway stations: receives the plurality of spread pilot signals from the relay communication station; and spectrally inverse-spreads reception signals of the plurality of spread pilot signals with a reception-side spreading code corresponding to the transmission-side spreading code, wherein any one of the gateway stations of the plural gateway stations or a common apparatus common to each gateway station: estimates the plural propagation path responses between the gateway station and the antenna for the feeder link of the communication relay apparatus in a transmission signal band of the feeder link, based on reception results of the plurality of inverse-spread pilot signals that are spectrally inverse-spread; calculates a weight for suppressing an interference signal that causes an interference by a transmission signal transmitted from the relay communication station to the gateway station and received by another gateway station, based on estimation results of the plural propagation path responses, with respect to each of the plural gateway stations; and transmits a calculation result of the weight to the relay communication station, wherein the feeder-link communication section of the relay communication station receives calculation results of the plural weights transmitted from the any one of the gateway stations or the common apparatus, and wherein the interference suppression section of the relay communication station adds or subtracts, for the transmission signal to be transmitted to the gateway station, a transmission signal to be transmitted to the other gateway station that is multiplied by the weight corresponding to the other gateway station, with respect to each of the plural gateway stations.
 6. The system according to claim 1, wherein the relay communication station comprises a feeder-link communication section that transmits and receives relay signals different from each other on the same frequency in the feeder link to and from the plural gateway stations, and an interference suppression section that suppresses an interference between plural feeder links formed with the plural gateway stations, wherein the plural gateway stations transmit a plurality of spread pilot signals that are spectrally spread with a plurality of transmission-side spreading codes orthogonal to each other, to the relay communication station, wherein the feeder-link communication section of the relay communication station: receives the plurality of spread pilot signals from the plural gateway stations; and spectrally inverse-spreads reception signals of the plurality of spread pilot signals with a reception-side spreading code corresponding to the transmission-side spreading code, and wherein the interference suppression section of the relay communication station: estimates the plural propagation path responses between the plural gateway stations and the antenna for the feeder link of the communication relay apparatus in a transmission signal band of the feeder link, based on reception results of the plurality of inverse-spread pilot signals that are spectrally inverse-spread; calculates a weight for suppressing an interference signal that causes an interference by a transmission signal transmitted from the relay communication station to the gateway station and received by another gateway station, based on the plural propagation path responses, with respect to each of the plural gateway stations; and adds or subtracts, for the transmission signal to be transmitted to the gateway station, a transmission signal to be transmitted to the other gateway station that is multiplied by the weight corresponding to the other gateway station, with respect to each of the plural gateway stations.
 7. The system according to claim 1, wherein the relay communication station transmits a plurality of spread pilot signals that are spectrally spread with a plurality of transmission-side spreading codes orthogonal to each other, and wherein the plural gateway stations: receive the plurality of spread pilot signals from the relay communication station; spectrally inverse-spread reception signals of the plurality of spread pilot signals with a reception-side spreading code corresponding to the transmission-side spreading code; estimate the plural propagation path responses between the gateway stations and the antenna for the feeder link of the communication relay apparatus in a transmission signal band of the feeder link, based on reception results of the plurality of inverse-spread pilot signals that are spectrally inverse-spread; calculate a weight for suppressing an interference signal that causes an interference by a transmission signal transmitted from the relay communication station to the gateway station is received by another gateway station, based on the plural propagation path responses; and add or subtract, for the reception signal received by the gateway station, a reception signal to be received by the other gateway station that is multiplied by the weight corresponding to the other gateway station.
 8. The system according to claim 1, wherein the plurality of spreading codes are orthogonal to each other, and wherein the plurality of pilot signals are transmitted and received at the same frequency.
 9. The system according to claim 1, wherein the plural pilot signals are transmitted and received by being distributed in plural guard bands located on both sides of the transmission signal band of the feeder link.
 10. The system according to claim 1, wherein the plural pilot signals are transmitted and received within the transmission signal band of the feeder link.
 11. The system according to claim 1, wherein the system estimates the plural propagation path responses and calculates the plural weights at a center frequency of the transmission signal band of the feeder link or a frequency around the center frequency.
 12. A relay communication station that is incorporated in an aerial-staying type communication relay apparatus and relays radio communication of a terminal apparatus, comprising: a feeder-link communication section that transmits and receives relay signals different from each other on a same frequency in a feeder link to and from plural gateway stations that are time-synchronized with each other; and an interference suppression section that suppresses an interference between plural feeder links formed with the plural gateway stations, wherein the feeder-link communication section: transmits a plurality of spread pilot signals that are spectrally spread with a plurality of transmission-side spreading codes orthogonal to each other, to the plural gateway stations; and receives estimation results of plural propagation path responses between the gateway stations and an antenna for the feeder link of the communication relay apparatus in a transmission signal band of the feeder link, wherein the estimation results are estimated based on reception signals of a plurality of inverse-spread pilot signals that are spectrally inverse-spread with a reception-side spreading code corresponding to the transmission-side spreading code by any one of the plural gateway stations or a common apparatus common to each gateway station, wherein the interference suppression section: calculates a weight for suppressing an interference signal that causes an interference by a transmission signal transmitted from the relay communication station to a gateway station and received by another gateway station, based on the plural propagation path responses received from the any one of the gateway stations or the common apparatus, with respect to each of the plural gateway stations; and adds or subtracts, for the transmission signal to be transmitted to the gateway station, a transmission signal to be transmitted to another gateway station that is multiplied by the weight corresponding to the other gateway station, with respect to each of the plural gateway stations.
 13. A relay communication station that is incorporated in an aerial-staying type communication relay apparatus and relays radio communication of a terminal apparatus, comprising: a feeder-link communication section that transmits and receives relay signals different from each other on a same frequency in a feeder link to and from plural gateway stations that are time-synchronized with each other; and an interference suppression section that suppresses an interference between plural feeder links formed with the plural gateway stations, wherein the feeder-link communication section: transmits a plurality of spread pilot signals that are spectrally spread with a plurality of transmission-side spreading codes orthogonal to each other, to the plural gateway stations; and receives reception results of the plurality of inverse-spread pilot signals, wherein the plural gateway stations spectrally inverse-spread a reception signal of the spread pilot signal with a reception-side spreading code corresponding to the transmission-side spreading code, and wherein the interference suppression section: estimates plural propagation path responses between the gateway stations and an antenna for the feeder link of the communication relay apparatus in a transmission signal band of the feeder link, based on the reception results of the plurality of inverse-spread pilot signals; calculates a weight for suppressing an interference signal that causes an interference by a transmission signal transmitted from the relay communication station to a gateway station and received by another gateway station, based on estimation results of the plural propagation path responses, with respect to each of the plural gateway stations; and adds or subtracts, for the transmission signal to be transmitted to the gateway station, a transmission signal to be transmitted to the another gateway station that is multiplied by the weight corresponding to the another gateway station, with respect to each of the plural gateway stations.
 14. A relay communication station that is incorporated in an aerial-staying type communication relay apparatus and relays radio communication of a terminal apparatus, comprising: a feeder-link communication section that transmits and receives relay signals different from each other on a same frequency in a feeder link to and from plural gateway stations that are time-synchronized with each other; and an interference suppression section that suppresses an interference between plural feeder links formed with the plural gateway stations, wherein the feeder-link communication section: transmits a plurality of spread pilot signals that are spectrally spread with a plurality of transmission-side spreading codes orthogonal to each other, to the plural gateway stations; and receives a calculation result of a weight for suppressing an interference signal that causes an interference by a transmission signal transmitted from the relay communication station to a gateway station and received by another gateway station, wherein the weight is calculated based on reception signals of a plurality of inverse-spread pilot signals that are spectrally inverse-spread with a reception-side spreading code corresponding to the transmission-side spreading code by any one of the plural gateway stations or a common apparatus common to each gateway station, with respect to each of the plural gateway stations, and wherein the interference suppression section adds or subtracts, for a transmission signal to be transmitted to the gateway station, a transmission signal to be transmitted to the other gateway station that is multiplied by the weight corresponding to the another gateway station, with respect to each of the plural gateway stations.
 15. An interference suppression method in a feeder link between a relay communication station and plural gateway stations, the relay communication station being incorporated in an aerial-staying type communication relay apparatus and relaying radio communication of a terminal apparatus, the plural gateway stations being time-synchronized with each other to transmit and receive relay signals different from each other on a same frequency, the method comprising: transmitting and receiving a plurality of pilot signals that are spectrally spread using a plurality of spreading codes orthogonal to each other between the relay communication station and the plural gateway stations; estimating a propagation path response between the plural gateway stations and an antenna for feeder link of the communication relay apparatus in a transmission signal band of the feeder link, based on reception results of spectral inverse-spreading the plurality of pilot signals; calculating plural weights respectively corresponding to the plural gateway stations based on the plural propagation path responses; and subtracting, from a signal to be transmitted and received via a directional beam corresponding to the gateway station, a signal to be transmitted and received via the directional beam corresponding to the other gateway station that is multiplied by the weight corresponding to the other gateway station, with respect to each of the plural gateway stations. 